List of Open Seminars

 
 

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Upkar Kumar Verma
Prof. Y. N. Mohapatra
Y8209064
Localized States in P3HT:PCBM based Bulk Heterojunction Device Structures
10th February 2016 (Wednesday)
12 noon
Samtel Center for Display Technologies (Seminar Room)
Blend of conjugated polymers and fullerene derivatives such as P3HT:PC60BM have emerged as model systems for organic photovoltaic applications. Device engineering and optimization has led to increase in the efficiency and stability of P3HT:PCBM solar cells over the past decades. However, there is a lack of understanding of physical mechanisms, specially the role of localized states in limiting performance and their electrical signature.
In this thesis, we seek to study possible manifestations of localized states in a variety of solar cell structures using P3HT:PCBM as the active material. We mainly used forward bias photo-capacitance response and open circuit voltage decay as tools among other conventional techniques. We demonstrate that useful information on deep localized states or recombination centers can be gained using this perspective.
We show that capacitance-voltage (C-V) characteristics in the first quadrant of current density-voltage (J-V) characteristics can be used as a probe to study the nature of defect states and their energetic distribution in conventional solar cell structures. Capacitance in space charge region is used to map the density of defect states distributed within the gap both under dark and white light illumination. The distribution parameters and the occupied density of defect states estimated as a function of temperature.
In order to isolate electron mobility and trapping mechanism in an otherwise bulk heterojunction material, electron only structures are fabricated and studied. Impedance spectroscopy is deployed to characterize the transport and storage of charge carriers in ITO|ZnO| P3HT:PCBM|Al (electron only) device. Complex part of impedance as a function of frequency is modeled to extract the mobility under dark and white light illumination. The defect states exposed under photo-excitation are interpreted as site service as dominant recombination centers. The recombination is mainly governed by Shockley Reed Hall recombination mechanism. The presence of recombination centre is further confirmed using the C-V characteristics. The mobility and capture cross-section are estimated as a function of temperature.
The photo-capacitance voltage characteristics of conventional as well as inverted solar cell incorporating P3HT:PCBM as active materials are modeled using the drift diffusion theory. The photo voltage and the carrier accumulation at the injecting interface are determined as a function of illumination intensity and compared for both structures.
Open circuit voltage decay transient have been used to identify internal loss mechanisms in P3HT:PCBM bulk heterojunction conventional and inverted solar cells. The transient describe using a model of decay based on a diode couple to a capacitor and a resistor. The diode ideality factor so obtain helps in the identification of dominant recombination mechanism. The diode current and dark shut current are isolated in the presence of excess carriers, and hence the intensity dependence of light induced recombination is determined independently for the two structures for comparison. The possible origins of such differences are discussed.


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Ms. Reeta Pant
Krishnacharya
Y9209066
Investigation of tunable wetting and slippery behavior on hydrophilic surfaces
Friday July 10, 2015
10:00 AM (tea @ 9:45 AM)
FB-382
Wetting of a liquid on a solid surfaces is one of the most common surface/interfacial phenomenon which can be primarily controlled by manipulating surface/interfacial energies and/or surface roughness. Here I demonstrate reversible switching of surface wettability using polystyrene/titania nanocomposite based responsive surfaces upon ultraviolet (UV) exposure and annealing. Static and dynamics of wetting transitions are investigated as a function of UV exposure, annealing temperature and time. Subsequently, the surface roughness was covered using an oil layer to prevent from Cassie to Wenzel transition which also acts as lubricant for enhanced slippery behavior. Slippage of water drops on smooth/rough hydrophilic surfaces will be discussed in details. Optimization of various experimental parameters will be presented to fabricate most efficient slippery surfaces in terms of performance and stability.


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Mr. Jitesh Barman
Krishnacharya
11109868
Electric Field Controlled Interfacial Phenomenon at Liquid-Solid/Liquid Interfaces
December 10, 2015 (Thursday)
11 am
FB-382
Wetting of liquids on solid surfaces is one of the most important interfacial phenomenon from fundamental as well as application point of view. Wettability of a surface can be controlled by manipulating the surface free energy of solids either passively by coating or actively using external stimulus e.g. temperature, radiation, electric filed etc. Here we report external electric field induced manipulation of liquids on solid and liquid surfaces. Electrowetting on dielectrics (EWOD) has been established as an effective tool to reversibly manipulate the surface wettability. Firstly I will talk about the application of EWOD in open-microfluidics. Surface grooves with triangular cross-section will be used as open-microfluidics. Static and dynamics of liquid transport in the grooves, actuated via electrowetting, will be discussed along with appropriate theoretical model. Subsequently, EWOD on dielectric lubricating fluid coated solid surfaces, to reduce hysteresis, will be presented. Nepenthes pitcher plants have motivated researchers to explore lubricating fluid coated slippery surfaces. I will demonstrate how using external electric field, electrically tunable slippery surfaces can be fabricated with electric field dependent slip velocity. Multiple aqueous droplets on such lubricating fluid coated surfaces show spontaneous coalescence or pseudo non-coalescence depending on the lubricating fluid film thickness. External electric field can also be used to control the coalescence or non-coalescence on such surfaces. Towards the end, I will talk about specially engineered superoleophobic surfaces which repel low surface tension liquid (oils and hydrocarbons). Ultraviolet radiation induced reversible wettability change, from superoleophobic to oleophilic, will also be discussed.


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Mr. Ambrish Pandey
Mahendra K. Verma
10109872
Scaling of large- and small-scale quantities in Rayleigh-Bénard convection
02-Dec-2015
11 am
FB-382
Thermal convection is responsible for heat transport in many natural systems, e.g., in stars, Earth's mantle, Earth's atmosphere, etc. We study Rayleigh-Bénard convection (RBC) in which a fluid placed between two horizontal plates is heated from below and cooled from top. Resulting motion of the confined fluid is primarily governed by the Prandtl number (Pr), a ratio of kinematic viscosity and thermal diffusivity, and the Rayleigh number (Ra), a ratio of buoyancy and viscous forces. The Nusselt number (Nu), a measure of the convective heat transport, and the Péclet number (Pe), a ratio of heat advection and heat diffusion, are important nondimensional parameters. We study the scalings of Nu(Ra,Pr) and Pe(Ra,Pr) by performing direct numerical simulations using pseudo-spectral solver Tarang. For Pr ≈ 1, we observe Nu ~ Ra0.27 and Pe ~ Ra0.50. However, Nu ~ Ra0.30 and Pe ~ Ra0.60 are observed for very large and infinite Pr. Moreover, for very large Pr the scalings of Nu and Pe are very similar in 3D and 2D RBC. We also study the scaling of kinetic energy and entropy spectra for very large Prandtl numbers. The kinetic energy spectrum scales with wavenumber (k) as k-13/3, and the entropy spectrum exhibits dual branches in the inertial range for both 2D and 3D simulations. The entropy flux remains constant in the inertial range for very large Pr.


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Mr. Gyanendra Kumar
R.Vijaya
Y9109068
Loss-modulated fibre ring laser and control of its dynamical features
05.11.2015 (Thursday)
10.30 am
FB-382
Highly-stable erbium-doped fibre amplifiers and lasers are useful in traditional fibre-optic communication due to their wavelength range of operation lying in the low-loss window of glass fibres. Fibre lasers operating in the chaotic domain are equally useful, but for widely disparate applications ranging from secure communication systems to chaos-based LiDARs and random number generation. An understanding of the conditions for switch-over from linear to nonlinear dynamical regime of fibre lasers, their tendency for chaotic operation, and possibilities of controlling their dynamics are essential for these applications. We study the fundamental as well as sub- and super-harmonic resonance characteristics of the erbium-doped fibre laser in the regime of its relaxation oscillation frequency, the evolution of its chaotic dynamics, and the conditions leading to its bi-stable and multi-stable operation using the cavity-loss modulation technique through experiments. For various modulation parameters, the laser exhibits different periodic states (period-1, period-2, period-4, etc) eventually leading to deterministic chaos through the period-doubling route. This work shows that we can repetitively drive the non-autonomous class-B laser into and out of linear, nonlinear (of different extents), and chaotic dynamics with a very simple approach as required for applications. The nonlinear oscillator model of the laser provides a good agreement between the theory and experiments. Convenient user-defined parameters such as the pumping ratio and the biasing voltage of modulation enable a fine control on the laser dynamics. The alternate technique of pump modulation is also analyzed for the sake of completeness, and the advantage of loss modulation is established.


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Mr. Rohit Kumar
Prof. Mahendra K. Verma
10109875
Energy transfers in dynamos with small and large magnetic Prandtl numbers
03.11.2015
11 am
FB-382
The presence of magnetic field in celestial bodies is explained by dynamo mechanism in which a conducting fluid in motion generates a self-sustained magnetic field. In dynamo, energy is transferred form velocity field to magnetic field and consequently the growth of magnetic energy takes place. The magnetic Prandtl number (Pm), the ratio of kinematic viscosity and magnetic diffusivity, is an important non-dimensional parameter for dynamos. We study energy transfers in dynamos with small- and large-Pm by performing direct numerical simulations (DNS) in a 3D periodic box on 10243 grid, using a pseudo-spectral solver Tarang. Energy fluxes and shell-to-shell energy transfers show that for dynamo with large-Pm, the growth of magnetic energy takes place due to nonlocal energy transfers from large-scale velocity field to small-scale magnetic field. For dynamo with small-Pm on the other hand, the magnetic energy grows due to local energy transfers from large-scale velocity field to large-scale magnetic field. We also use a shell model of dynamo to understand the energy transfers for extreme values of Pm, which are otherwise inaccessible to DNS due to the computational constraints. The energy fluxes in our shell model simulation are in qualitative agreement with the DNS results. We also construct a low-dimensional model to study the dynamo transition for very small to very large Pm and observe that the critical magnetic Reynolds number for dynamo transition, Rmc, saturates to constant values in the two limiting cases of Pm.


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Ms. Shraddha Sharma
Dr. Amit Dutta
Y9209067
Fidelity and Loschmidt echo: Quenches, non-analyticities and emergent thermodynamics
30/09/2015 (Wednesday)
11 am
FB-382
Our work focuses on relating quantum information theoretic measures such as the ground state fidelity and the Loschmidt echo (LE) to quantum phase transitions (QPTs) and dynamics. Fidelity is the modulus of the static overlap of the two ground states of a system at different parameter values; whereas, the LE is the modulus of the overlap of two states evolved from the same initial state with two different Hamiltonians. Therefore, one can map a connection between the two; both the tools effectively detects the quantum critical point (QCP) and follows universal scaling behavior close to it. Since, QPTs are low energy phenomena, (i.e., the gap is minimum for the low energy modes) the major contribution to the fidelity and the LE comes from these low energy modes. We shall explore the situation in which these tools fail to mark a QCP and address the question that in what situations high energy modes makes dominant contributions. In this so-called marginal situation, we shall explain how one ends up in a logarithmic scaling behavior of the fidelity. Furthermore, we shall introduce and analyze a quantity referred to as the dynamical fidelity (which is a version of the LE) obtained for a periodically driven quantum Hamiltonian. Exploring the entire regimes of the frequency and the number of periods, we shall show how it differs from any other thermodynamic observable obtained for a periodic Hamiltonian. We shall also explore dynamical phase transitions (DPT) using the LE as a tool for both sudden and slow quenching of an integrable quantum system; extending the work further to a non-integrable system, we shall explain the presence and the absence of DPTs by exploring the underlying integrability of the Hamiltonian. Also, we shall exhibit how the LE emerges as an useful measure not only to detect the QCP but also to investigate the work statistics at zero and finite temperature of a quenched system. Exploring the finite temperature LE, we shall further study the emerging thermodynamics and observe the behavior of the average irreversible work and the irreversible entropy in a many body quantum system following a sudden quench and propose their scaling behavior.


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Gopal
Dr. Pankaj Jain
Y9109066
Cosmological and Colliders Implications of Conformal Symmetry
29/09/2015 (Tuesday)
4 pm
FB-382
Symmetry has always played an important role in understanding Nature. At present most of our theoretical knowledge comes from the symmetry principles. In this talk I will discuss the implications of scale or conformal symmetry. In particular, I will propose a possible solution to the fine tuning problem of cosmological constant within the framework of softly broken conformally symmetric model. Cosmological constant is potentially a source of Dark energy, which constitutes about 70% of the energy density of the Universe. A major problem with the cosmological constant is that it gets very large quantum contributions from the matter sector at each order in perturbation theory. So we need to cancel these large contributions in order to maintain the small value of observed dark energy density, leading to an acute fine tuning problem. In our proposed solution we have shown that the matter sector will not contribute to the cosmological constant and hence we have solved the fine tuning problem. Here we have not considered the quantum gravity effects since quantum theory of gravity is not well formulated.


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Shubhankar Das
Z. Hossain & R.C. Budhani
Y9109078
Magnetoresistance and Magnetothermopower studies of delta-doped
2-dimensional electron gas at the interface of LaTiO3/SrTiO3
30th April, 2015
11 am
FB-382
Abstract: Studies of the 2-dimensional electron gas (2DEG) at the interface of LaAlO3 (LAO) or LaTiO3 (LTO) and TiO2 terminated SrTiO3 (STO) has attracted much attention in recent years due to its interesting properties like metal-insulator transition, magnetism, superconductivity and strong spin-orbit interaction effects in the electronics transport. We have used a new approach to bring about modification in the electronic properties of this 2DEG. This involves delta (δ) doping at the interface of LTO/STO by an iso-structural antiferromagnetic perovskite (TN = 298 K) LaCrO3 (LCO). This δ-layer dramatically alters the properties of the 2DEG. The changes includes increase in room temperature sheet resistance (R□), drop in the sheet carrier density (n□) almost linearly with the layer thickness, and emergence of new features in the temperature dependence of R□ at T ≤ 50 K. Our spectroscopic measurement along with density functional theory (DFT) calculations show that the Cr-ions at the interface act like a trap for electrons which are transferred from the LTO to STO surface. Extensive measurements of out-of-plane and in-plane magnetoresistance (MR) have been carried out on all the samples to address issue such as weak antilocalization and Kondo scattering. We have also observed a gradual crossover from positive out-of-plane MR to negative in-plane MR when magnetic field is titled with respect to the film surface. The MR measurements are augmented by the measurement of thermopower (S) which increases dramatically with δ-layer thickness at ambient temperature. The linear temperature dependence of S in the temperature range 100 to 300 K is indicative of diffusion thermopower. We also observed a large enhancement in thermopower in the temperature range where a minimum in R□ is observed. This enhancement is attributed to Kondo scattering. The thermopower is suppressed in the presence of a magnetic field and the suppression is isotropic with respect to the field direction. We will also present a tunable Rashba S-O interaction in these interfaces by δ-doping with another iso-structural ferromagnetic perovskite LaCoO3 (LCoO). In LCoO-doped sample, the inelastic scattering time varies as 1/T and the S-O scattering time remains constant in temperature, which suggests that the spin relaxation follows the D’yakonov-Perel mechanism. The δ-doping also results in 3 order of magnitude decrease in τso whereas the inelastic scattering time increases very slowly with doping. A detailed analysis of anisotropic MR when the field is applied in the plane of the sample displays the effects of Zeeman interaction with conduction electron spin.


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Reeta Pant
Krishnacharya
Y9209066
Investigation of tunable wetting and slippery behavior on hydrophilic surfaces
10th July, 2015
10 am
FB-382
Wetting of a liquid on a solid surfaces is one of the most common surface/interfacial phenomenon which can be primarily controlled by manipulating surface/interfacial energies and/or surface roughness. Here I demonstrate reversible switching of surface wettability using polystyrene/titania nanocomposite based responsive surfaces upon ultraviolet (UV) exposure and annealing. Static and dynamics of wetting transitions are investigated as a function of UV exposure, annealing temperature and time. Subsequently, the surface roughness was covered using an oil layer to prevent from Cassie to Wenzel transition which also acts as lubricant for enhanced slippery behavior. Slippage of water drops on smooth/rough hydrophilic surfaces will be discussed in details. Optimization of various experimental parameters will be presented to fabricate most efficient slippery surfaces in terms of performance and stability.


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Dushyant Kumar
Prof. R. C. Budhani and Prof. Z. Hossain
Y9109064
Spin and electronic charge diffusion in superconducting NbN and disordered  SrTiO3 under the influence of magnetic field and light
29th June, 2015
11 am
FB-382
Spin-based electronics generally called “spintronics” encodes and processes information in the quantum-mechanical spin of the electrons leading to reduced power consumption with faster operation. However, the generation of pure spin currents, its transport and detection remain a challenge. A comprehensive understanding of these phenomena requires study of spin diffusion in metals, semiconductors and superconductors. It has been of fundamental interest to search for the sources of pure spin currents and the materials which can allow long spin diffusion lengths. In this thesis work we have addressed both these issues. We used the full Heusler alloy Co2MnSi (CMS) as a source of polarized spins. This Heusler compound is a half metallic ferromagnet. Such a band structure suggests 100% spin polarization, thus making the ordered cubic phase of Co2MnSi a good candidate for spintronic devices. As for the material for efficient transport of spin current, we have concentrated on SrTiO3, a cubic band insulator well known for its useful dielectric and opto-electronic properties. The high mobility (∼2 x 103 cm2/Vs at 15 K) electron gas was induced in the few nanometer thickness of STO by irradiating its surface using Ar+-ions. The process converts ~4 nm thick surface layers of STO into a metal while over the remaining thickness of a 0.5 mm wafer remains insulating. The unperturbed base material has been used as a gate dielectric in a back gated geometry.

The NbN was used to study the effect of spin polarized current in superconductors. It is a BCS type of superconductor with high bulk critical temperature (TC ~ 16 K) and large upper critical field (>20 Tesla). The NbN thin films with fairly high TC (~15 K) was grown at relatively low growth temperature (~2000C) making this material possible to integrate with hybrid structures. Devices have been fabricated to study the spin diffusion in superconducting NbN as well as in metallic Ar+-ion irradiated STO (reduced STO).

The spin-polarized current (IS) injection into the superconductor drives it out of equilibrium and results in an excess quasi particle density, which leads to the suppression of the superconducting gap. This effect is realized in the form of suppression of superconducting critical current (IC). The IS-injection from CMS into NbN shows a large (≈67%) suppression of IC at T/TC ≈ 0.4. This correspond to a large dynamic gain, Gd = -dIC/dIS, of 36 at 3 K. A control device, Au/MgO/NbN, is also made to rule out the Joule heating effect.

The spin transport through reduced STO was studied in a Co-based 3-terminal device. The spin injected from one Co-electrode was allowed to diffuse through the surface electron gas of reduced STO and detected on the other Co-electrode located 10µm far from the injector. The change in resistance while ramping the magnetic field from positive to negative suggest that the reduced STO could remember the spin for 10µm distance.

For device perspective of the surface electron gas of reduced STO, it is desirable to study its response to photon and electrostatic fields. In this connection, we have studied the photoconductivity (PC) and photoluminescence (PL) of ion irradiated STO and tuned them using electrostatic gate field. The reduced STO showed a large UV sensitive persistent photoconductivity over the temperature range of 300 to 15 K, with a relaxation time of several hours. Interestingly, at 300 K, a negative gate field accelerates the post-illumination recovery process pushing the system to relax to its ground state quickly. This property has the potential for designing a solid state photoelectric switch. The PL spectra of the reduced STO showed multi-color emission at room temperature, whose intensity increases gradually with decreasing temperature with a sharp increase below 80 K. At 20 K, the negative as well as positive gate field is observed to increase PL intensity. These properties have been addressed in the light of structural phase transition in SrTiO3.

 
 [1] Dushyant Kumar, P. C. Joshi, Z. Hossain, and R. C. Budhani, APL 102, 112409 (2013)

 [2] Dushyant Kumar, Z. Hossain, and R. C. Budhani, PRB 91, 205117 (2015)



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Date:
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Shubhankar Das
Z. Hossain & R.C. Budhani
Y9109078
Magnetoresistance and Magnetothermopower studies of delta-doped
2-dimensional electron gas at the interface of LaTiO3/SrTiO3
30th April, 2015
11 am
FB-382
Abstract: Studies of the 2-dimensional electron gas (2DEG) at the interface of LaAlO3 (LAO) or LaTiO3 (LTO) and TiO2 terminated SrTiO3 (STO) has attracted much attention in recent years due to its interesting properties like metal-insulator transition, magnetism, superconductivity and strong spin-orbit interaction effects in the electronics transport. We have used a new approach to bring about modification in the electronic properties of this 2DEG. This involves delta (δ) doping at the interface of LTO/STO by an iso-structural antiferromagnetic perovskite (TN = 298 K) LaCrO3 (LCO). This δ-layer dramatically alters the properties of the 2DEG. The changes includes increase in room temperature sheet resistance (R□), drop in the sheet carrier density (n□) almost linearly with the layer thickness, and emergence of new features in the temperature dependence of R□ at T ≤ 50 K. Our spectroscopic measurement along with density functional theory (DFT) calculations show that the Cr-ions at the interface act like a trap for electrons which are transferred from the LTO to STO surface. Extensive measurements of out-of-plane and in-plane magnetoresistance (MR) have been carried out on all the samples to address issue such as weak antilocalization and Kondo scattering. We have also observed a gradual crossover from positive out-of-plane MR to negative in-plane MR when magnetic field is titled with respect to the film surface. The MR measurements are augmented by the measurement of thermopower (S) which increases dramatically with δ-layer thickness at ambient temperature. The linear temperature dependence of S in the temperature range 100 to 300 K is indicative of diffusion thermopower. We also observed a large enhancement in thermopower in the temperature range where a minimum in R□ is observed. This enhancement is attributed to Kondo scattering. The thermopower is suppressed in the presence of a magnetic field and the suppression is isotropic with respect to the field direction. We will also present a tunable Rashba S-O interaction in these interfaces by δ-doping with another iso-structural ferromagnetic perovskite LaCoO3 (LCoO). In LCoO-doped sample, the inelastic scattering time varies as 1/T and the S-O scattering time remains constant in temperature, which suggests that the spin relaxation follows the D’yakonov-Perel mechanism. The δ-doping also results in 3 order of magnitude decrease in τso whereas the inelastic scattering time increases very slowly with doping. A detailed analysis of anisotropic MR when the field is applied in the plane of the sample displays the effects of Zeeman interaction with conduction electron spin.


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Nikhil Kumar
Anjan Kumar Gupta
Y9109074
Control of the thermally hysteretic regime in superconducting weak-links and quantum interference devices
21st Apr 2015 (Tuesday)
11:30 am
FB-382
Micron size-Superconducting Quantum Interference Devices (micro-SQUIDs) are the most suitable probes for nano-scale magnetism. Hysteresis in the current-voltage characteristics of such devices has been a limiting factor and my thesis explores ways to restrict this hysteretic regime. We have fabricated and studied the current-voltage characteristics of a number of Nb film based weak-link devices and SQUIDs showing a critical current and at least two re-trapping currents. We have proposed a new understanding for the re-traapping currents in terms of thermal instabilities in different portions of the device. We also find that the superconducting proximity effect and the phase-slip processes play an important role in dictating the temperature dependence of the critical current. The proximity effect also helps in widening the temperature range of hysteresis-free characteristics. Finally we demonstrate a control on temperature-range on hysteresis-free characteristics in two ways: 1) By using a parallel shunt resistor in close vicinity of the device, and 2) by reducing the weak-link width. Thus we demonstrate non-hysteretic regime down to 1.3 K temperature, which is usually restricted to 1-2 K below the critical temperature (~ 9 K, for Nb). We have also studied the SQUID oscillations with magnetic flux in both the hysteretic and non-hysteretic regimes.


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Bappa Saha
Sutapa Mukherji
10109063
Work distribution, entropy production and fluctuation theorems in
nonequilibrium systems
20th April, 2015 (Monday)
11 am
FB-382
Out of equilibrium processes are the most observed phenomena in the natural world. The presence of a nonzero flux of the energy or matter across  the   system, a nonzero entropy production in the surrounding medium are some of the special features of  nonequilibrium processes. In addition, nonequilibrium systems exhibit interesting phenomena such as
boundary induced phase transition, spontaneous symmetry breaking, unusual critical behavior etc. Recently, there have been many efforts to characterize the nonequilibrium processes through a set of powerful theorems, known as fluctuation theorems (FT). The emphasis of FTs have been on quantifying the asymmetry between the probability distributions in the forward and time-reversed processes for the thermodynamic
quantities, such as entropy production, work done by external force etc.

In this talk, we shall study an asymmetric simple exclusion process(ASEP), a nonequilibrium process that involves  driven motion of many particles on a one dimensional lattice. We show how the boundary induced phase transitions exhibited by this process can be systematically analyzed  using a fixed-point based boundary layer analysis. In the next part of my talk, using the  Onsager-Machlup functional integral approach, we discuss the work and heat distribution functions for a Brownian particle subjected to an oscillatory driving force. We verify whether these distributions satisfy FTs. Following the same line of approach, we next obtain the work distribution function for a Brownian particle subjected to a nonconservative force. Although the work distribution has a Gaussian form, it is found that the distribution does not satisfy the conventional work fluctuation theorem. In the last part of the talk, we   discuss the entropy production and the associated fluctuation theorem for an ASEP with two sites and elucidate how the computation of the average entropy production rate plays a central role in characterizing the steady states of such non-equilibrium systems.


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Gangadhar Behera
S. Anantha Ramakrishna
Y9109065
Nanostructured Plasmonic thin films for enhanced optical properties
16th April, 2015 (Thursday)
11 am
FB-382
The unique optical properties of nano-structured plasmonic films have attracted great attention due to their potential applications in solar cells, photo-detectors, sensors, nano-imaging devices, thermal emitters and many more. Surface plasmon polaritons (SPPs) are surface electromagnetic waves that exist at the interface between a metal and a dielectric material. In this work, the significant role of the surface plasmons in understanding novel optical phenomena like enhanced transmission or enhanced absorption in nano-structured plasmonic thin films is investigated in detail. The extra-ordinary transmission of light through an array of holes in thin plasmonic films for use as conducting transparent electrodes is proposed. By experiments and simulations, these structured metallic electrodes are also shown to enhanced absorption for solar cell applications. Complementary layers of ladder-like plasmonic structures fabricated by laser interference lithography (LIL) are investigated for enhanced optical properties in the visible-IR bands. Possible applications as polarization dependent sensors at IR frequencies is also discussed.

Enhanced absorption from a trilayer plasmonic system consisting of structured hole arrays in gold film separted from the bottom gold layer by dielectric spacer is reported. The fabrication by LIL and optical characterization of these samples are presented. A new approach to design dual band perfect absorber in the visible to the NIR region with top metallic patches on a SiO2 coated Si substrate is reported. A physical model for these absorbers is presented. A combined structuring of metallic disc and grating arrays on glass substrates that give rise to triple-band perfect absorption at visible frequencies is also reported. The physics behind these enhanced phenomena are discussed.  The results have good potential for realizing low-cost large area nanostructured plasmonic thin film devices for energy applications.


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Dheeraj Pratap
S. Anantha Ramakrishna
Y9109063
Anisotropic and Hyperbolic Metamaterials in the cylindrical geometry
30th March,  2015 (Monday)
4 pm
FB-382
Metamaterials are artificial structured composites, which have properties not usually found in natural materials. Electromagnetic metamaterials can be designed to  show, for example, extreme anisotropy where the dielectric permittivity tensor components can even have opposite signs. In natural anisotropic crystals, the anisotropy is usually a very small fraction of the permittivity. The large anisotropy in metamaterials is attractive for novel applications ranging from super-resolution lenses to super-radiative sources due to the hyperbolic dispersion of modes. Oriented plasmonic nanowire assemblies and multilayers of alternating metallo-dielectric films are the common examples that show anisotropic behaviour. Fabrication of nanowire metamaterials is usually accomplished by electro-deposition of the metals into the nanopores of a nanoporous alumina template.

Nanoporous alumina microtubes in the cylindrical geometry have been developed by anodizing microwires of aluminum. These microtubes have nanopores radially emanating from the centre towards the periphery. These microtubes represent a new class of anisotropic optical fibers that have different kinds of modes described by uncommon Bessel functions with imaginary orders. This is due to the hyperbolic mode dispersion in these systems. Electro-deposition of plasmonic nanowires into the nanopores make hyperbolic disperison easily accessible. A homogenization of the nanostructure in the cylindrical geometry has been carried out using techniques of transformation optics. A detailed analysis of the mode structure and mode dispersions has been carried out.

Light scattering and absorption studies from nanoporous alumina surfaces in the flat and cylindrical geometries are reported here.  Flouresence studies of molecules deposited on these nanoporous alumina surfaces with and without metallic inclusions in them are presented. Some unique applications of these alumina surfaces to thermal engineering will be mentioned.


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Govind Dayal Singh
Y9109067
Metamaterials for Infra-red Multi-spectral Absorbers
18th March, 2015 (Wednesday)
3:30 pm
FB-382
Electromagnetic absorbers have wide applicability and need to be impedance matched with free space to reduce the reflectance from their surface. Here we discuss the design and fabrication of metamaterials that show multi-band perfect absorbances at infra-red frequencies. The key a highly absorbing medium is to choose resonant structures that simultaneously have matched electrical and magnetic resonances. An array of metallic (conducting) particles separated from a conducting ground plane by a dielectric spacer layer constitutes the resonant structure. Proper choice of the particle size and layer thickness can result in perfect absorption that is reasonably independent of the excitation angle and polarization. Use of multi-layered stacks of particles that can also yield multi-band absorption. While most metamaterial designs utilize the fundamental mode in a sub-wavelength sized resonator, highly localized higher order modes can also be utilized for multi-band perfect absorption.
Multi-band metamaterial absorbers based on fundamental as well as higher order resonances for Infra-red frequencies have been designed, fabricated and characterized. The metamaterial absorbers have multiple absorption bands across the MWIR and LWIR bands with peak absorbances exceeding 90%. Metamaterial absorbers, with broadband absorption at the mid-infrared frequencies and high transmittance at visible frequencies, have been fabricated using a semiconductor Indium Tin Oxide (ITO) film as the ground plane.The metamaterials were fabricated by simple, cost-effective laser micromachining techniques, shadow mask deposition and oblique angle deposition technique. A strategy to tune or switch the metamaterial absorption by incorporated a phase change material such as VO2 in the metamaterial has been implemented and results in a thermochromic metamaterial.


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Abstract:

Pranati Rath
Y9109077
Large Scale Anisotropy in Cosmic Microwave Background Radiation and its Dependence on the Primordial Power Spectrum
20th March, 2015 (Friday)
11:30 am
FB-382
The Cosmological principle says that the universe at large distance scale is assumed to be statistically homogeneous and isotropic. The Cosmic Microwave Background Radiation (CMBR) is considered to be one of the best experimental evidence supporting this principle. However, there exists considerable evidence in cosmological data which suggests violation of this principle.
In this talk, I will revisit two of these anomalies observed in the CMBR temperature data provided by WMAP and recently by PLANCK team. These includes the alignment of the quadrupole (l=2) and octopole (l=3) and the hemispherical power asymmetry. To explain the low-l alignment, I will discuss some anisotropic inflationary models within the framework of the Big Bang cosmology. In these models, the anisotropy decays very quickly during the inflationary phase of expansion. The resulting direction dependent power spectrum in this anisotropic background leads to violation of isotropy and hence explain the alignment of the low l CMBR modes.
I will also discuss an inhomogeneous power spectrum model in order to explain the hemispherical power asymmetry, observed in the CMBR data. The hemispherical asymmetry can be parametrized in terms of the dipole modulation model. Alternatively, I will show that, an anisotropic dipolar imaginary primordial power spectrum, which is possible within the framework of noncommutative space-times, also provides a good description of the observed dipole modulation in CMBR data.


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Tutul Biswas
10109877
Wave packet dynamics and phonon scattering in spin-orbit coupled fermionic systems.
9th March, 2015 (Monday)
11 am
FB-382


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Subhash Mahapatra
10109069
Applications of the Gauge-Gravity duality : Superconductivity,
holographic Optics and Entanglement Thermodynamics.
10th February, 2015 (Tuesday)
11 am
FB-382
A remarkable connection, in the context of string theory, has emerged in last few years between gravity and the strongly coupled field theories. This connection, which is generally called as the AdS/CFT correspondence or the gauge/gravity duality, maps a quantum theory of gravity in (d +1) dimension Anti de sitter (AdS) spacetime to d dimensional conformal field theory (CFT) - living at the boundary of AdS spacetime. An important feature of this duality is that in certain approximation, the strongly coupled limit of field theory corresponds to the weakly coupled limit of the gravity theory. This strong-weak nature of the correspondence has provided a unique approach to address some questions in strongly coupled condensed matter systems which otherwise would be intractable.

In this thesis, we discuss applications of the AdS/CFT correspondence, on three main directions: superconductivity, optics and entanglement thermodynamics.

We generalize the minimal models of holographic superconductors in a gauge invariant way and explore the rich phase structure of the boundary theory. Then, we study the electromagnetic response functions and entanglement entropy of these generalized holographic superconductors for various space-time geometries.


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Uday Bhanu Paramanik
Y8109071
Magnetism and superconductivity of Eu-based "122" pnictides.
6th February, 2015 (Friday)
11 am
FB-382
The discovery of high-temperature superconductivity in Iron pinctides has created enormous interest leading to the finding of a wide range of layered pnictide compounds which exhibit a rich variety of magnetic and transport phenomena. Among the '122' pnictides, EuFe2As2 got particular attention as this system demonstrates interesting interplay between superconductivity and local moment magnetism of Eu moments. We have investigated the effect of Iridium doping on the magnetic and superconducting properties of EuFe2As2. The optimal Iridium doping suppresses the Fe antiferromagnetic order and induces superconductivity below 22 K. The Eu moments order magnetically at ~18K with strong ferromagnetic (FM) component. The competition between the superconducting and the magnetic state leads to the reentrance of superconductivity. While the superconducting properties of the Fe-As based materials have been studied extensively, very recently, unconventional superconductivity has been discovered in the vicinity of antiferromagnetic order in a class of CrAs based compounds. We present the synthesis and physical properties of a new compound EuCr2As2 in the '122' pnictide family which exhibits  antiferromagntic ordering of Cr itinerant moments in addition to the ferromagnetic order of Eu local moment. This behavior is reminiscent of the parent compound of Fe based superconductor EuFe2As2 but with a slightly different magnetic structure. Furthermore, since the valence fluctuations in classical heavy-fermion systems are considered to be responsible for unconventional superconductivity, we discuss the important aspect of the evolution of magnetism upon Ge-doping in the valence fluctuating heavy fermion compound EuNi2P2. The rare-earth ion configuration changes from valence fluctuating (VF) state in EuNi2P2 to nearly integral valence Eu2+ (4f7) in EuNi2PGe which orders antiferromagnetically below TN = 12 K. No superconductivity was observed in the Ge-doped EuNi2P2 down to 2K.


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Bahadur Singh
Y9209061
Electronic structure and spin texture of non-trivial surface states
of topological insulators
28th Jan. 2015 (Wednesday)
4:0 pm
FB-382
A new paradigm for classifying condensed matter systems by topology of bulk band structure has spurred the discovery of several new states of matter having exotic properties. In particular, topological insulators are such new states of matter that are distinct from conventional insulators. These materials support spin-polarized conducting states at the boundaries/surfaces while remaining insulating in the bulk. The surface states often exhibit Dirac-cone energy dispersion with helical or chiral spin-texture and are protected by time reversal symmetry. The topological protection ensures the backscattering free transport at the boundaries of topological insulators. The recent developments in the field show that these nontrivial states not only offer potential applications in quantum computing and spintronics, but also provide platforms for realizing novel quantum phenomena such as Weyl semimetals, and Majorana fermions in a condensed matter system.

In this work, we present an analysis of topological surface state properties of several selected materials and predict new materials or thin films of materials that realize the quantum spin Hall state, Dirac semimetal, Weyl semimetal, or Rasbha effect, using the ab-initio density functional theory framework and k.p theory. Through systematic analysis of bulk and surface electronic structures, we show that thallium based ternary III-V-VI2 series of compounds, TlMQ2 (where M= Bi or Sb and Q= S, Se, or Te), contain both topological and normal insulators and therefore, it is possible to study the topological phase transition (TPT) by tuning the lattice parameters as well as spin-orbit coupling (SOC). The electronic structure and spin-texture analysis of topological surface states show that the surface states form an unusual “planer metal” that is essentially half of an ordinary two dimensional (2D) conductor and carry nontrivial π Berry phase. Furthermore, we discuss possible TPT in Ge(BixSb1-x)2Te4 thin films as a function of layer thickness and Bi concentration x. The systematic examination of band topologies suggests that thin films of Ge(BixSb1-x)2Te4 are viable candidates for 2D topological insulators, which would undergo a 2D-TPT as a function of x. Finally, our analysis shows that the inversion asymmetric compound, Sb2Se2Te, harbors both a novel nontrivial band topology and giant Rasbha-type spin splitting in its native form driven by strong SOC. The Rasbha splitting in the bulk bands of Sb2Se2Te is the largest that has been found to date and attributed to large polarization field (electric field), which arises from the broken inversion symmetry in the system.

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Abstract:

Jhuma Dutta
Y9109069
Photonic and Plasmonic properties of Periodically Patterned Columnar Thin Films
26 November, 2014 (Wednesday)
11 am
FB-382
Columnar thin films are known to be deposited by making incident a collimated vapor flux at  arge oblique angles to a substrate. Using a substrate that is periodically patterned at icro/nanoscales, new kinds of periodically patterned columnar thin films (PP-CTFs) have been fabricated. The extremely anisotropic optical properties offered by the nanocolumnar structure with larger scale structures for photonic bandgap or diffractive effects provide for new physical phenomenon. These structures were also found to be extremely reconfigurable giving rise to enormous flexibility in applications.

The PP-CTF of various dielectrics like CaF2/ MgF2/SiO2 and metals like silver are shown to be conveniently fabricated by this method. The complete morphology of the PP-CTF is shown to be determined by controlling the angle and flux rate of depositions. PP-CTFs are shown to have enhanced photonic and plasmonic properties. Dielectric PP-CTFs are shown to function as blazed diffraction gratings with large asymmetric diffraction efficiencies. A CTF made of plasmonic metals like silver renders it an effectively biaxially anisotropic continuum. PP-CTFs of silver showed strong blazing action and asymmetrically coupled optical radiation to surface-plasmon-polariton(SPP) waves for both p- and s- polarizations propagating only along one direction supported by the CTF/dielectric interfaces.

The blazing effect of the gratings of dielectric CTFs as a result of the spatially linear phase shifts caused by prismatic air cavities was understood using Kirchhoff-Fresnel diffraction theory. Homogenization of the metallic CTFs using the Bruggeman formalism revealed them to display hyperbolic dispersion, and the dispersion of SPP waves on both 1D and 2D gratings of such anisotropic hyperbolic media was found to be adequately described thereby. Detailed electromagnetic simulations of the grating structures reveal large changes in the photonic properties with the slant angle such as diffraction efficiencies and the electromagnetic near fields. Furthermore, these slanted nanocolumnar structure can be uniformly reconfigured by ion beam irradiation method and gives rise to reconfigurable blazed gratings, thereby maximizing the diffraction efficiencies for different wavelength bands by changing the blazing (angle) condition. A novel application using superstructures of CTFs to fingerprint visualization was developed. Visualization of latent fingerprints is enhanced by deposition of columnar thin films at large oblique angle of CaF2 and SiO2 on fingerprint marks on two nonporous surfaces such as smooth glass slides and highly reflecting rough aluminum sheets and further enhanced visualization is obtained by treating the deposited CTFs with a fluorescent dye and fluorescence imaging.


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Sourabh Barua
Y7109075
Electrical transport studies of topological insulator
materials.
24th November, 2014
11:30 am
FB-382
Topological insulators are a class of materials which have generated great interest due to their novel properties. The band structure of these materials has surface bands which span the bulk band gaps and the crossing of these bands at the time reversal invariant momentum is protected as long as time reversal symmetry is not broken. This ensures that the materials have a conducting surface despite possessing an insulating bulk. However experimental verification of these surface states in electrical transport studies has been difficult due to the fact that the bulk itself conducts due to defects. In the work done for this thesis we have performed electrical transport studies of the topological insulator materials Bi2Te3 , Sb2Te3 and Bi(2-x)Sb(x)Te(3-y)Se(y). In Bi2Te3, in spite of a metallic bulk, we observe signatures of a topological surface state from the non-zero Berry phase extracted from the Shubnikov-de Haas(SdH) oscillations in the magnetoresistance in addition to a large and linear magnetoresistance. Further angle dependent magnetoresistance studies have revealed interesting asymmetry for positive and negative fields for some angles although the SdH oscillations are more or less symmetric. Sb2Te3 shows initially a negative magnetoresistance which evolves with time to a positive one but the same SdH oscillations persist. There is also asymmetry in the positive and negative fields. In Bi(2-x)Sb(x)Te(3-y)Se(y)we obtained metallic single crystals which showed linear magnetoresistance. We have also made a comparison of the thickness dependence of resistivity reported for various topological insulators in literature with a simple model.


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Anirban Dutta
Y7109062
Temperature dependent scanning tunneling microscopy and spectroscopy (STM/S) studies of Iron-Arsenic based single crystals.
21st October, 2014 (Tuesday)
3 pm
FB-382
Iron-Arsenic (FeAs) based superconductors with high critical temperature have a spin ordered ground state with a spin density wave (SDW) order. Superconductivity emerges in close proximity to the SDW state by suppressing (or weakening) SDW order, thus the SDW order is found to anti-correlate with the superconducting order. My thesis work focuses on the variable temperature scanning tunneling microscopy and spectroscopy (STM/S) studies of AFe2As2 (A: rare earth or alkaline earth element), i.e. 122-series, compounds. We have studied two undoped parent compounds, EuFe2As2 and SrFe2As2, and two doped compounds, CaFe1.96Ni0.04As2 (underdoped) and SrFe1.6Co0.4As2 (optimally doped) with STM/S. The tunnel spectra show homogeneous energy gap in the undoped and underdoped crystals in the SDW state. However, we see spatially inhomogeneous spectra in the SC state in underdoped and optimally doped crystals. We observe an asymmetric suppression in densty of states only at some locations in the SC state for the underdoped crystal, while the optimally doped crystals show a superconducting gap everywhere with spatially varying magnitude. Moreover, for the undoped SrFe2As2 crystals, strength of the SDW gap weakens below 21K, where a small fraction superconducts as found from resistivity and suscptibility measurements. This compound could be more prone to superconducting order and small local perturbations, like strain, may nucleate superconductivity locally in this undoped crystal. Finally we discuss the posiible reasons behind the observed inhomogeneous superconducting state.

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Samit Paul
Y8209868
Micron Focusing, Diagnostics and Interaction of Multi-Element Ion Beams with Matter
22nd September, 2014 (Monday)
12:00 noon
FB-382
A focused ion beam (FIB) system is an inevitable tool for research and applications in nano-science and technology. However, the availability of only gallium (Ga) ions as projectile, in liquid metal ion source (LMIS) based FIB systems limits its applicability. Moreover, metallic Ga has contamination issues and provides less milling yield. In order to ameliorate the above problems, an emerging area in this field is development of focused ion beams of a variety of elements utilizing plasmas. A compact, high current density (~ 1 A/cm^2), microwave plasma based multi-element focused ion beam (MEFIB) system has been developed in the laboratory, i.e., capable of delivering beams of different ions (H2, Ar, Kr, Ne) of energies up to 18 keV and spot size of ~ 25 µm, using a 1 mm plasma electrode (PE) aperture. The beam has an emmittance of ~ 0.1 mm-mrad and brightness of ~ 10^5 Am-2sr-1V^-1, thereby making it an excellent candidate for FIB.

In this thesis our target has been to reduce the beam to submicron spot size and make it operate at higher energies (30 keV) comparable to that of conventional FIBs. In parallel, we developed a new diagnostics (spider probe) for measuring micron size beams and have investigated the time dependent physics of the interaction with matter, particularly, the milling capability to make micro-pores and microstructures on metallic foils and thin films.

In order to achieve the above, first the plasma has been optimized to maximize the extracted beam current density maintaining tolerable ion energy spread at the meniscus (~5 eV). The utilization of two Einzel lenses in conjunction with a PE and a beam limiting (BL) aperture, is found to have better control over the beam energy and current density. Controlled sculpting of micron scale pores in aluminum foil with Ar and Kr ion beams is demonstrated. The temporal evolution of the micro pores caused by beam interaction on metallic foils has been studied and smallest pore diameter of ~ 3 µm has been successfully created. This shows that with proper control of the irradiation time, submicron pores can be fabricated. Further experiments, using smaller PE apertures of 45 µm and 31 µm, created by MEFIB, have been used to obtain a focused beam size ~ 1 µm. A time-dependent exposure method to determine the exact location of the focal point of the beam has been invented that takes care of the over irradiation issue. Extensive use of Lab-View software is made to create the microstructures on 50 nm Cu thin films.

In order to reduce the beam spot size further, guiding and transmission of extracted Ar ion beams with the help of straight and tapered micro-glass-capillary have been investigated. The beam current through the capillary is found to have a threshold extraction voltage and observed to exhibit hysteresis, with a unique self-focusing capability. The temporal and dimensional dependence of the hysteresis have been studied. The guiding capability of the tapered capillary is found to be more effective where beam size reduction is desired without compromising total beam current unlike electrostatic beam limiters. For further understanding the phenomena, Particle-In-Cell simulations that solves Poisson's equation and equation of motion self consistently are carried out, and the experimental results are found to have a reasonable agreement with simulations.


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Abstract:

Ms. Vandana Yadav
Y9109082
Polymerization dynamics of microtubules: A boundary layer based approach
4th September, 2014
2:30 pm
FB-382
Microtubules are important components of the cytoskeleton of a cell. These are hollow, tube shaped biopolymers made of alpha,beta-tubulin heterodimers. Experimental studies reveal that microtubules alternate between persistent phases of polymerization and depolymerization. Since microtubules play an important role in various processes such as intracellular organisation, transport, exerting pushing and pulling forces etc., it is crucial to understand the polymerization dynamics of microtubules and its regulations by various other proteins.

In the first part of my seminar, I shall discuss a two-state model of microtubule polymerization with a length-dependent dynamics and obtain the length distributions of microtubules through a discrete formulation.

Next, I shall discuss the boundary layer method and show how it can be used to understand phases and phase transitions of driven many-particle exclusion processes. We develop a fixed point based boundary layer method and apply this to two distinct driven exclusion models to show how the shape of the particle distribution profile, the location of the boundary layer etc can be predicted from the stability properties of the fixed points of the boundary layer equation.

In the last part of my seminar, I shall use the boundary layer method to understand the polymerization dynamics of microtubules in the presence of diffusing tubulins. Since various rates associated with the polymerization dynamics are expected to be influenced by the number of available tubulins, the growth dynamics and the diffusive dynamics of tubulins are coupled in a nonlinear way. The boundary layer analysis emerges as a powerful method that allows us to obtain analytical solutions for the length distributions in a systematic way.


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Anirban Bagui
Y7109861
Effect of electric field annealing during solvent-drying of polymer layers.
30.07.2014 (Wednesday)
4:15 pm
SCDT seminar room
Controlling the nano-morphology of organic active layers for improved organic electronic devices has recently attracted immense attention. In this thesis the changes in the polymer film properties due to thermal annealed during the solvent drying in the presence of a constant electric field across the film are studied. Comparative studies of morphological and electro-optic properties of the P3HT: PCBM based blend film and bulk hetero-structure devices have been carried out to understand the role of this electric field annealing. The external quantum efficiency (EQE) and power conversion efficiency (PCE) of the solar cells made from the electrical field annealed films were found to be significantly enhanced due to better charge transport in the films.

In order to study the effect of electric-field on the mobility of P3HT, single carrier devices were made. The hole mobility in P3HT was found to increase monotonically with electric field strength up to 2E5 V/m. The J–V data corresponding to the space charge limited currents (SCLC) at low temperatures for P3HT based hole-only devices were fitted with the empirical model and Gaussian disorder model (GDM) for modeling the charge transport so as to interpret the findings of the XRD measurements. These confirmed an increase in crystallinity and crystallite size of the films for electric-field annealed samples.

Solar cells with the 'inverted structure' were fabricated to see if improvement in devices performance can be achieved by electric-field annealing of their active layers. Finally, electric–field assisted treatments were carried out on some other polymer - PTB7, PCDTBT, MEHPPV - layers and the effect of the treatments on the mobility in the films were studied.

In this thesis, the application of electric fields across the active layer of organic solar cells at the time of its formation has been shown to help achieve higher mobility polymer films for building devices that have improved performance.


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M. Hemanadhan
Y8209866
Study of excited-state energy density functionals constructed by splitting k-space for homogeneous electron gas
2.6.2014 (Monday)
4:00 pm
FB-382


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Abstract:

Jaidip M. Jagtap
Y8109066
Polarimetry, Optical and Fluorescence Confocal Microscopy: Study and Discrimination of Human Cervical Precancerous Tissue
2.5.2014 (Friday)
11.00 am
Biological tissue displays morphological and biochemical changes during transformation to diseased state. Optical techniques are ideal for minimally invasive detection of such changes. Light scattering has been seen to capture morphological changes, such as increase in size and density of nuclei in cells. Subtle precancerous (dysplasia) changes are probed via Mueller matrix imaging which strongly manifest in the depolarization power and retardance and are seen to differ significantly in normal and dysplastic tissues sections. Fluorescence Mueller matrix spectroscopy has been developed recently for measurements from the connective tissue regions of human cervical tissue and reveal intriguing fluorescence diattenuation and polarizance effects. The estimated fluorescence linear diattenuation and polarizance parameters were considerably reduced in the precancerous tissues as compared to the normal ones, which were also confirmed by control experiments.

Robust statistical parameters in the form of moments, specifically weighted mean, full width at half maxima, standard deviation, skewness, kurtosis and pixel counts characterizing these distributions are shown to unambiguously distinguish microscope captured images of various tissue types. Combining these parameters effectively improves the diagnosis and classifies quantitatively various classes of tissue. Optical spatial frequency spectra from different stages of human Cervical Intraepithelial Neoplasia (CIN) tissue are also evaluated as a potential quantitative pathological tool on confocal captured images. The degree of randomness of tissue structures from normal to different stages of CIN tissue can be recognized by spatial frequency analysis.

Fluctuations in the elastic light scattering spectra of normal and dysplastic human cervical tissues through wavelet transform based techniques have been analyzed and reveal clear signatures of self-similar behavior in the spectral fluctuations. The strong dependence of the elastic light scattering on the size distribution of the scatterers manifests in the angular variation of the scaling exponent. These findings using the multi-resolution analysis capability of the discrete wavelet transform can contribute to the recent surge in the exploration for non-invasive optical tools for pre-cancer detection.

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Rajyavardhan Ray
Y5209066
Disorder and Correlation Effects on a Honeycomb Lattice:
Application to Graphene
14th June 2013 (Friday)
11 am
FB-382


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Venue:

SK Firoz Islam
Y8109070
Electronic and magnetotransport properties of spin-orbit coupled two-dimensional
electron system.
7th June, 2013 (Monday)
11:00 am
FB-382


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Time:

Venue:

Amit Banerjee
Y7209864
Resonance behavior of FIB grown nanomechanical systems and the
role of microstructure
23rd April, 2013 (Tuesday)
9 AM
FB-382


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Venue:

Pabitra Mandal
Y6109067
Anomalous magnetic response of CaFe1.94Co0.06As2 superconductor and nonlinear response of the driven vortex state in NbS2 superconductor.
25th April, 2013 (Thursday)
11 am
FB-382


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Time:

Venue:

Suman Banerjee
Y5209865
Optoelectronic modelling of organic solar cells
12th March, 2013 (Tuesday)
5:15 PM
Samtel Centre Seminar Room


Speaker:
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Date:

Prince Gupta
10209064
Metamaterials and plasmonics with active gain medium

10/10/2012, 4:00-5:00 PM


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Date:
Time:
Venue:

Mr. Gyanendra Singh
Y5109067
Spin reorientation transition and superconductivity in NbN based ferromagnet-superconductor thin film heterostructures.|
9th Fubruary, 2013 (Saturday)
12 pm - 1 pm
FB-382

Speaker:
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SOTA Title:
Date:

Sunil Kumar
Y9109079
Multiple Quantum wells in Organic Semiconductors

03/01/2012,Tuesday


Speaker:
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OS Title:
Date:

Mr. Gyanendra Singh
Y5109067
Spin reorientation transition and superconductivity in NbN based ferromagnet-superconductor thin film heterostructures.
23rd December (Friday), 2011


Speaker:
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OS Title:
Date:

Pavan Aluri
Y5109071
Large Scale Anomalies in the Cosmic Microwave Background Radiation
Thursday 1st December, 2011


Speaker:
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OS Title:
Date:

Ms. Anupam
Y6209061
Magnetic and Superconducting Properties of Novel Eu-based Arsenide and Gallide
29th November (Tuesday), 2011


Speaker:
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OS Title:
Date:

Naveen Kumar Singh
Y5109070
Scale Invariance and its Cosmological Implications
Thursday 20th October, 2011


Speaker:
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SOTA Title:
Date:

Bahadur Singh
Y9209061
Electronic band structure and Z2 topological Invariant of topological Insulators

September 16, 2011 (Friday)


Speaker:
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SOTA Title:
Date:

Ms. Reeta Pant
Y9209066
Responsive surfaces with tunable wetting properties and study of the wetting transition

8th September, 2011 (Thursday)


Speaker:
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SOTA Title:
Date:

Shraddha Sharma
Y9209067
FIDELITY APPROACH TO QUANTUM PHASE TRANSITION & QUENCHING

9th September 2011 Time: 1200 hrs


Speaker:
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SOTA Title:
Date:

Mr. Lalruatfela
Y9109071
Imaging in Random Media using Diffuse Light

12th August, 2011 (Friday)

Speaker:
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OS Title:

Date:

Dheerendra Yadav
Y4209861
SPECTROSCOPIC AND IMAGE DIAGNOSTICS OF LASER ABLATED PLASMA PLUME FOR ION AND ATOMIC SOURCE
November 29, 2010 (Monday)


Speaker:
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OS Title:
Date:

Indranuj Dey
Y5209863
Wave Interaction with Plasmas Confined in Multicusp Magnetic Fields
November 29, 2010 (Monday)


Speaker:
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OS Title:
Date:

Vijay Kumar Bisht
Y3809069
Studies on non-equilibrium magnetic behavior of antiferromagnetic oxide nanoparticles
November 29, Monday


Speaker:
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SOTA Title:
Date:

Dushyant Kumar
Y9109064
Heusler alloy based magnetic tunnel junctions

9th December (Thursday)


Speaker:
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SOTA Title:
Date:

Ms. Vandana Yadav
Y9109082
Driven Exclusion Processes in Physics and Biology: Models and Analysis

8th Dec, 2010


Speaker:
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Date:

Upkar Kumar Verma
Y8209064
Memories based on Quantum Dot Embedded Organic Semiconductors

Tuesday 16/11/2010


Speaker:
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Date:

Jhuma Dutta
Y9109069
DESIGN,FABRICATION AND CHARACTERIZATION OF PHOTONIC SCULPTURED THIN FILMS
10 November 2010 (Wednesday)


Speaker:
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SOTA Title:
Date:

Prabhakar Tiwari
Y9109075
Cosmic Ray anisotropy studies at the GRAPES observatory (Ooty).

November 3, 2010 (Wednesday)


Speaker:
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SOTA Title:
Date:

Govind Dayal Singh
Y9109067
Metamaterials for tunable multi-spectral absorbers

October 25, 2010 (Monday)


Speaker:
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OS Title:
Date:

Mr. Sunil Kumar Mishra
Y4109075
Size-dependent magnetization fluctuations and slow dynamics in NiO nanoparticles.
September 15, 2010 (Wednesday)


Speaker:
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OS Title:

Date:

Mr. Shyam Kumar Choudhary
Y4809063
Scanning Tunneling Microscopy and Spectroscopy Studies of Electronic Inhomogeneities in Graphite and Graphene
August 30, 2010 (Monday)


Speaker:
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SOTA Title:
Date:

Ashutosh Sharma
Y8209062
Electronic Structure of Topological Insulators

Sep 4, 2010


Speaker:
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SOTA Title:
Date:

Mr. Samit Paul
Y8209868
Submicron focusing, diagnostics and interaction of multi-element ion beams with matter

May 17, 2010 (Monday)


Speaker:
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OS Title:
Date:

Awnish Kumar Tripathi
Y3809065
Photo-electronic Properties & Localized States in Polymeric Semiconductors
7th May (Friday), 2010


Speaker:
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OS Title:

Date:

Devendra Kumar
Y280962
Non-equilibrium features in the solid state: A case study of the transition metal oxide NdNiO3
05-05-2010


Speaker:
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OS Title:
Date:

Jaivardhan Sinha
Y4209862
Properties of magnetic materials under extreme conditions
03-5-10(Monday)


Speaker:
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SOTA Title:
Date:

Anup Kumar Singh
Y8109062
Study of Electrical and optical properties of Indium Gallium Zinc Oxide: A novel amorphous oxide semiconductor
April 28, 2010 (Wednesday)


Speaker:
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OS Title:
Date:

Anurag Sahay
Y220961
Thermodynamic Geometry, Phase Transitions and Critical Phenomena in AdS black holes
23.04.2010


Speaker:
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Date:

Mr. Asrarul Haque
Y4109069
Causality in Nonlocal Quantum Field Theory, Noncommutative Quantum Field Theory and 1+1 Dimensional Yukawa Model
23rd April 2010 (Friday)


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Jose V Mathew
Y5109069
Multi-element focused ion beams from intense microwave plasmas
13th April, 2010 (Tuesday)


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Pankaj Kumar Mishra
Y3809066
Instabilities and Turbulence in Rayleigh-Bénard Convection: Numerical and Phenomenological studies
12th April, 2010 (Monday)


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Mr. Debjit Datta
Y4809062
Study of optical and morphological properties of thin films in CuPc/C60 solar cells
26th March 2010 (Friday)


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Jaidip Manikrao Jagtap
Y8109066
Mueller Imaging in Turbid Media and Human Tissues

15th March, 2010 (Monday); 11:00 AM (Tea at 10: 45 AM)


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Sk Firoz Islam
Y8109070
Electronic and transport properties of graphene

March 11, 2010 (Thursday)


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Ms. Sangeeta Chakrabarti
Y5209067
Controlling MetaMaterials with Radiation and Controlling Radiation with Metamaterials
8th March, 2010


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Ajeet Kumar Sharma
Y8109061
Stochastic mechanics of molecular motors on nucleic acid strands

February 11, 2009 (Thursday)


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Mr. Mihir Sarkar
Y7209062
Tailoring the Optical Properties of Materials Using Ion Beams

27th Jan, 2010


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Amit Banerjee
Y7209864
Fabrication and Characterization of Nano Sensors using Focused ion beam

28th Jan, 2010.


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Ms. Arpana Prasad
Complex Magnetic Behaviour of Ce-, Pr-, Eu- and Yb-based Compounds
18th December (Friday), 2009


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Bhupendra Nath Tiwari
Y220961
Correlations, Stabilities and Black Holes in String Theory and M-Theory
04 November, 2009 (Wednessday)


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Sarvesh Kumar Tripathi
Y6109862
Investigation of focused ion beam induced processes and their utilization for nanofabrication
5th November, (Thursday)


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Ashok Garai
Y4109078
Molecular motor transport and traffic: effects of individual mechanochemistry and steric interactions
4th November, 2009 (Monday)


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Pramoda Kumar Samal
Y3209064
TESTING STATISTICAL ISOTROPY OF COSMIC MICROWAVE BACKGROUND RADIATION
October 19, 2009, (Monday)


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Bhaskar Kamble
Y4809061
A Quantum Expansion Parameter for Metallic Ferromagnets: Orbital Degeneracy, Hund's Coupling, and Quantum
Friday, 9 Oct 2009


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Himanshu Pandey
Y7109069
SPIN POLARIZATION AND SPIN DEPENDENT TUNNELING IN HEUSLER ALLOYS
September 29, 2009


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Nitul Singh Rajput
Y7209063
Fabrication of micro and nano structures by focused ion beam and their science and technology applications
September 30, 2009


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Surajit Sarkar
Y7109876
Oxide/CNT Heterostructures & Secondary Electron Emission

September 23, 2009


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Ankur Rastogi
Y7109063
Carrier Modulation by Field Effect and Electronic Phase Transitions in Perovskite Oxides

September 25, 2009


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Shail Kumari
Y7209063
Interaction of modulated electromagnetic waves with a pre-ionized medium

September 23, 2009


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Sourabh Barua
Y7109075
Dynamical studies of phase transitions in ferroelectrics and multiferroics

25 Sptember, 2009


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Surajit Sarkar
Y7109876
Oxide/CNT Heterostructures & Secondary Electron Emission

23 Sptember, 2009


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Uma Divakaran
Y4209864
Slow quenching dynamics in quantum critical systems
22 Sptember, 2009


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Abhishek Chowdhury
Y7209061
Generation and studies of multi-element single and multiple focused ionbeamlets from an intense wave assisted plasma for creation of functional surfaces
17 Sptember, 2009


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Prasanna Kumar Rout
Y7209866
Proximity Effect in Superconductor-Normal Metal and Superconductor-Ferromagnet Hybrids
14 Sptember, 2009


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Anirban Dutta
Y7109062
STM/STS Studies of Strongly Correlated Systems

09 Sptember, 2009


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Date:

Ajeet Kumar Sharma
Y8109061
Stochastic mechanics of molecular motors on nucleic acid strands

February 11, 2009 (Thursday)


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Debaprasad Sahu
Y7109067
Negative ions: Volume generation, measurement and wave induced phenomena

4 May, 2009


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Prasanta Kumar Muduli
Y3109063
Spin polarized transport in planar structures and tunnel junctionsof perovskite oxides
23 April, 2009


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Anirban Bagui
Y7109861
Annealing Effects on Organic SolarCell Performance

31 March, 2009


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Shyam Mohan
Y4109074
Instabilities in the vortex state of a type II superconductor
31 March, 2009


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Vinod Chandra
Y3109068
Hot QCD Equations of state and Quark-Gluon Plasma in Heavy ion Collisions
23 March, 2009


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Date:

Udai Raj Singh
Y4109077
Low Temperature Scanning Tunneling Microscopy and Spectroscopy Study of ManganiteThin Fimls
4 March, 2009


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Date:

Shyam Lal Gupta
Y6209062
Experimental and Theoretical Studies of Strongly
Correlated Systems

3 March, 2009


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Subhayan Mandal
Y280966
Pseudoscalar-Photon Mixing & It's Astrophysical Implications
23 February, 2009


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Md. Shamim
Y6209861
Exchange and correlation energy functionals in excited-state densityfunctional theory

6 February, 2009


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Lipsa Nanda
Y3209063
Energy flow approach to propagation of electromagnetic pulses through highly dispersive media
27 January, 2009


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Prashant Shukla
Y210964
Polarization Gated Imaging and Mueller Imaging in Turbid Media and Human Tissue
28, November 2008


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Tripti Tripathi
Y3809068
Template-Dictated Polymerization of Bio-Polymers: Machines and Mechanisms
26, November 2008


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Victor Mukherjee
Y6209864
Defect production and entropy generation in generalized quenching dynamics of spin systems
24, October 2008


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Sudhakar Pandey
Y210965
Correlated Electron Spin Dynamics in Metallic Ferromagnets
October 24, 2008


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Subhadip Mitra
Y280965
Two Photon Exchange Contributions to Elastic ep Scattering in the Non-local Field Formalism
September 24, 2008


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Gorky Shaw
Y6209863
Investigation of magnetic properties of superconducting nanostructures

September 22, 2008


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Pabitra Mandal
Y6109067
Effect of doping and disorder on superconducting properties

September 22, 2008


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Samar Layek
Y6209862
Investigations of Novel Rare Earth Compounds Using Magnetization, Electrical Resistivity and
Mössbauer Spectroscopy
August 20, 2008


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Somdutta Mukherjee
Y6109072
Electrical, Magnetic and Optical properties of multiferroic bulk and thin films
August 19, 2008