Speaker:

Prof. Sayan Kar

Affiliation:

IIT Kharagpu

Title:

Eddington-inspired Born-Infeld gravity

Date:

27th March 2014, Thursday

Time:

4 pm

Venue:

FB - 382

Speaker:

Dr. Sinu Mathew

Affiliation:

NUSNNI-NanoCore and Dept. of Electrical and Computer Engineering, National University of Singapore

Title:

The Effects of MeV Proton Irradiation on Interface Two-Dimensional Electron Gas (LaAlO₃/SrTiO₃) and Layered Solids (MoS₂,graphene)

Date:

3rd March 2014, Monday

Time:

12:00 pm - 1:00 pm.

Venue:

FB - 382

Abstract:

The two-dimensional electron gas (2DEG) formed at the interface between two band insulators LaAlO₃ (LAO) and SrTiO₃ (STO) is one of the most fascinating systems in the field of oxide research. Tailoring of the conductivity of this interface 2DEG is a challenge for the practical
applications of this system. MeV Proton irradiation on LAO/STO system is found to manipulate interfacial conductivity by carrier localization and eventually producing an insulating ground state by tailoring the defect structure of the substrate STO. The results of electrical and magneto-transport, Raman spectroscopy and spectroscopic ellipsometry will be discussed^[1]. The second part of the talk will be on the effects of MeV Proton irradiation on Molybdenum disulphide and graphene. MoS₂ a diamagnetic layered solid, is found to show ferrimagnetic ordering at room temperature when exposed to 2 MeV proton beam^[2]. A disorder mode corresponding to a zone-edge phonon and a valency of Mo higher than +4 have been detected in the irradiated samples. The stability of supported and suspended graphene under MeV Proton irradiation will also be discussed^[3].

References
1. S. Mathew, A. Annadi, T.K. Chan, Teguh Citra Asmara, D. Zhan, Ariando, A. Rusydi, Z.X Shen, M.B.H. Breese and T. Venkatesan. ACS Nano 7 (2013) 10572
2. S. Mathew, K. Gopinadhan , T.K. Chan, X.J. Yu, D. Zhan, L. Cao, A. Rusydi, M.B.H. Breese, S. Dhar, Z.X. Shen, T. Venkatesan and John TL Thong. Appl. Phys. Lett. 101 (2012) 102103
3. S. Mathew, T.K. Chan, D. Zhan, K. Gopinadhan, A.R. Barman, M.B.H. Breese, S. Dhar, Z.X. Shen, T.Venkatesan and John TL Thong. Carbon 49 (2011) 1720; J. Appl. Phys. 110 (2011) 84309

Speaker:

P. Santhana Raman (Post-doctoral fellow at Institute of Physics, Bhubaneswar)

Affiliation:

Centre for Ion Beam Applications, Department of Physics, National University of Singapore, Singapore

Title:

Research and Development with Energetic Broad- and Nano- Ion Beams:From Ion Beam Analysis to Novel Materials Modification and Proton Beam Writing Systems

Date:

24th February, 2014 (Monday)

Time:

3:30 pm - 4:30 pm.

Venue:

FB - 382

Abstract:

The process that can be accomplished using energetic ion beam technique broadens itself with no limit. Starting from routine materials analysis (via various Ion beam analysis technique), the advent of ion beam extends to carve and alter structures at nano scale, with nano-sized ion beam, to form novel materials. The cause and the effect of these energetic ion beams on both materials and soft-tissues are of paramount importance in understanding it in terms of both fundamental and application point of view. This talk will cover the Ion beam analysis techniques that were crucial in novel materials synthesis (especially with embedded InN and ZnO nanoclustres in silica matrix). The systematic approach, using energetic ion beams, in producing surface patterns will be discussed in the light of basic physics and its applications. Later in the talk I will introduce and explain about the next generation lithographic technique, namely Proton Beam Writing and its capability to produce high aspect ratio nanostructures. The developmental activities involved in making of high brightness ion source, to be used in next generation compact proton beam lithography, with a promise to deliver sub-10 nm beam spot size, will also be discussed.

Speaker:

Dr. Haraprasanna Lenka (Post-doctoral fellow at Institute of Physics, Bhubaneswar)

Title:

Microscopic characterization of GaN heterostructures using RBS/C and TEM: A comparative study.

Date:

January 16th, 2014 (Thursday)

Time:

4:00 pm - 5:00 pm.

Venue:

FB - 382

Abstract:

Recently, the success of the growth of high quality c-GaN layers on Si substrate has attracted considerable academic and commercial interest, because it can facilitate the integration of microelectronics and optoelectronics. But the large lattice and thermal mismatch between GaN and Si introduces a lot of dislocations which pose a major obstacle in the production of defect-free layers, much needed for device applications. Hence, material processing requires intermediate monitoring to quantitatively track the amount of defects formed during growth. Apart from measuring the critical characteristics like the dislocation density,
a good estimation of strain and composition is also important for device optimization. To meet this challenge, ion channeling is a very attractive and a powerful technique because of its unique mass sensitivity to the type of defects separately (such as point defects, dislocations, stacking faults or defect clusters). Results of RBS/C will be presented as a fast and non-destructive technique to analyze the defect density and the elastic strain, two parameters which can potentially affect the device performance in comparison with TEM results.

Speaker:

Debanjan Chowdhury (Harvard University)

Title:

Unconventional phases of quantum matter

Date:

January 15th, 2014 (Wednesday)

Time:

11:00 am - 12:00 pm.

Venue:

FB - 382

Abstract:

Theorists have been studying unconventional states of quantum matter over the past few years and starting recently, experiments on such states have finally appeared, generating much excitement. I will describe experimental observations on high temperature superconductors and magnetic insulators and their influence on our theoretical understanding. In the first part of the talk, I will introduce the theory of quantum criticality in metals and apply it to the phase diagrams of the high temperature superconductors. I'll review some of the experiments on the iron pnictides, which point toward the possible existence of a quantum critical point underneath the superconducting dome and try to offer a partial explanation for some of the mysterious observations^[1]. In the second part of the talk, I'll review some recent experiments on a kagome lattice anti-ferromagnet and argue that many of the observed features can be explained by the presence of fractionalized excitations in a quantum spin liquid^[2].

[1] D. Chowdhury, B. Swingle, E. Berg and S. Sachdev, Phys. Rev. Lett. 111,
157004 (2013).
[2] M. Punk, D. Chowdhury and S. Sachdev, Nature Phys. (to appear), 2014;
arXiv:1308.2222.

Speaker:

Dr. Sanjay Kumar Mandal (NIT Agartala)

Title:

Multiferroic Composites for Magnetic Field Sensors.

Date:

December 9th, 2013

Time:

11:30 am - 12:30 pm.

Venue:

FB - 382

Abstract:

Multiferroics with two or more ferroic (ferroelectric, ferro/ferri/anti-ferromagnetic, ferroelastic) orderings have attracted considerable attention in recent years. Single-phase multiferroics are rare and their magnetoelectric (ME) responses are either weak or occur at temperatures too low for practical applications. Ferromagnetic-piezoelectric composites, however, show strong ME coupling at ambient temperatures. The ME effect is a property mediated by elastic
deformation. The composites show a rich variety of phenomena including giant low-frequency ME interactions. 

This presentation will focus on recent developments in the physics and applications of composite multiferroics. The discussion will include our work on functionally graded composites for use as ultra sensitive magnetic field sensors.

Speaker:

Dr. Aditya Kelkar (TIFR, Mumbai)

Title:

Ion collisions with molecules and Clusters

Date:

January 8th, 2014 (Wednesday)

Time:

4:00 pm - 5:00 pm.

Venue:

FB - 382

Abstract:

The description of the temporal and spatial evolution of systems of mutually interacting particles is of fundamental importance in atomic collision physics. Theoretically the difficulty of this task lies in the fact that the Schrödinger equation is not analytically solvable for more than two particle systems even when the underlying forces are precisely known. On the other hand collisions with photons and charged particles (electrons and heavy ions) have proved to be excellent tools to investigate the structural and dynamical properties of physical systems like atoms, molecules, clusters and solid surfaces etc. The dynamics can be studied in a wide range of Coulomb interaction strength and time scales by suitable choice of heavy ion beams, offering the opportunity to study a multitude of processes such as ionization and capture, radiative and non-radiative relaxation etc to coherence effects and collective behaviour in many body systems as well as bond formation and rearrangement in chemical reactions.

In this talk I shall discuss the interaction of heavy ions with many body systems taking two examples from my research work. In the first part, I will describe collisions of highly charged heavy ions with fullerene C₆₀ in the intermediate velocity (v_p ~ 10 a.u.) range, focusing on the excitation of a collective surface plasmon mode known as Giant dipole plasmon resonance or GDPR. In this velocity range the dwell time of the projectile ion is ~10^-17 seconds and the interaction can be treated in the perturbative regime. However, in collisions at very low energy (v_p ~ 0.01 a.u.) the interacting particles have sufficient time for electronic rearrangement and bond formation leading to chemical reactions. In particular I will discuss the dynamics of a bimolecular nucleophilic substitution reaction between F - (anion) and CH₃Cl in gas phase using velocity map imaging (VMI) technique.

Speaker:

Dr. Arijit Saha (University of Basel, Switzerland)

Title:

Novel Transport phenomena in hybrid junctions of Nanowires

Date:

January 7th, 2014 (Friday)

Time:

2:45 pm - 3:45 pm.

Venue:

FB - 382

Abstract:

In the first part of the talk I shall give a brief introduction to my field of research called "Mesoscale and Nanoscale Physics" highlighting the subfield of low dimensional systems with examples and experiments. In the next part, I shall talk about transport properties of hybrid superconducting junctions of one dimensional n a no wi r es (NW). In particular, I shall demonstrate possible scenarios for production of pure spin current through such junctions. I shall also show that (a) effects due to inclusion of electron-electron interaction induced back-scattering in the wire, and (b) competition between the charge transport via the electron and hole channels across the junction give rise to a non monotonic behavior of the sub gap conductance as a function of temperature. ln the last part of the talk I shall introduce NW in the presence of Rashba spin orbit interaction, uniform magnetic field, and spatially modulated magnetic field. Such fully gapped system can support fractional fermion (FF) bound states at the two ends of the NW. I shall discuss the transport and noise signatures of such FF bound states which has never been investigated so far in literature.

Speaker:

Dr. Jaivardhan Sinha (National Institute for Materials Science (NIMS), Tsukuba, Japan)

Title:

Perpendicular magnetic anisotropy and current induced effective field in Ta(N)|CoFeB|MgO 

Date:

December 6th, 2013

Time:

12:00 pm - 01:00 pm.

Venue:

FB - 382

Abstract:

Perpendicular magnetic anisotropy (PMA) originating from the interface in Heavy metal(Pt, Ta)|Ferromagnet(Co, CoFeB)|Oxide structure (Al2O3, MgO) is of great interest because of its potential application in spintronics based devices. The recent finding of spin-orbit torque (spin Hall spin torque) in these heterostructures [1,2] has increased its significance manifold as it allows one to manipulate magnetization direction using in-plane current. Solid understanding the role of Heavymetal|Ferromagnet interface and Ferromagnet|Oxide interface is essential for utilizing them in application. In this talk I shall discuss the Ta|CoFeB interface properties in Ta(N)|CoFeB|MgO and the current induced effective field likely generated due to spin Hall effect from Ta. In general, Ta is known for creating a magnetic dead layer when placed next to a magnetic layer. As the CoFeB layer thickness is of the order of 1 nm to obtain PMA, thus it is desirable to have negligible magnetic dead layer from the point of view of thermal stability. The effect of Nitrogen doping in Ta underlayer on interface anisotropy, magnetic dead layer thickness and current induced effective field will be also discussed [3].

References:
    [1] Junyeon Kim, Jaivardhan Sinha, Masamitsu Hayashi, M. Yamanauchi, S. Fukami, T. Suzuki, S. Mitani and Hideo Ohno, Nature. Materials. 12, 240 (2013).

    [2] L. Liu, C. F. Pai, Y. Li, H. W. Tseng, D. C Ralph, and R. A. Buhrman, Science 336, 555 (2012).
    [3] Jaivardhan Sinha et al, Appl. Phys. Lett. 102, 242505 (2013).

Speaker:

Dr. Shibabrata Nandi (Jülich Centre for Neutron Science & Peter Grünberg Institute)

Title:

Structure, magnetism and superconductivity in Fe-based
superconductors

Date:

November 27th, 2013

Time:

11:30 am - 12:30 pm.

Venue:

L8 (LHC)

Abstract:

In iron-based high-temperature superconductors, magnetic fluctuations and magneto-elastic effects are believed to be important for the superconducting electron pairing mechanism. To gain insight into the interplay between the different ordering phenomena and the underlying couplings we studied the magnetic order and lattice distortion on AFe₂As₂ (A = Ca, Sr, Ba, Eu) single crystals by neutron and x-ray diffraction. High-resolution x-ray diffraction and neutron scattering measurements reveal an unusually strong response of the lattice and ordered magnetic moment to superconductivity in Co-doped BaFe₂As₂ . We propose that the coupling between lattice and superconductivity is indirect and arises due to the magnetoelastic coupling, in the form of emergent nematic order, and the strong competition between the magnetism and superconductivity. For the P-doped EuFe₂As₂ , coexistence between the ferromagnetism and superconductivity was observed and explained in terms of formation of a spontaneous vortex state.

Speaker:

Dr. Ajay Soni (School of Basic Sciences, IIT Mandi, Himachal Pradesh)

Title:

Nanocomposites of Layered Chalogenides for
Thermoelectric Applications

Date:

November 26th, 2013

Time:

12:15 Pm - 1:15 pm.

Venue:

L9 (LHC)

Abstract:

Research in the field of thermoelectricity (TE) is full of outstanding ideas, the materials having properties of an electron-crystal-phonon-glass, such as rattling semiconductors, alloys, heterostructures, and bulk-nanocomposites have shown to be efficient TE materials. In this context, the nanocomposites of layered chalcogenides (Te and Se) and pnictogen (Bi and Sb) materials have been preferably studied for their high-performance TE properties arising due to layered structure and narrow band gap.¹ The efficiency of the TE material is quantified by a dimensionless thermoelectric figure of merit, $ZT = S^2\sigmaT/\kappa$, where S is the Seebeck coefficient, $\sigma$ is the electrical conductivity, $\kappa$ is the thermal conductivity and T absolute temperature. Thus the interplay of the three physical parameters makes the problem very complex for TE materials. The research talk will focus on a novel class of solution grown Bi₂Te_3-xSe_x nanoplatelet composites (NPCs) having an enhanced thermoelectric properties² , and the effects of the thermodynamic environment during spark plasma sintering.³ For the case of NPCs, the grain boundaries and interfaces are playing important role such that the charge carriers and phonons couple in a unique fashion. The subtle understanding of the interface crystallization, grain growth and filtering of electron and phonons will be discussed. A brief notion on the family of layered materials and their technological aspects will also be emphasized.

References:
   1. Dresselhaus, M. S., Adv. Mater. 2007, 19, 1043-1053.
    2. Soni, A.; Yanyuan, Z.; Ligen, Y.; Aik, M. K. K.; Dresselhaus, M. S.; Xiong, Q., Nano Letters 2012, 12 (3), 1203.
    3. Soni, A.; Yiqiang, S.; Ming, Y.; Yanyuan, Z.; Ligen, Y.; Xiao, H.; Zhili, D.; Aik, M. K. K.; Dresselhaus, M. S.; Xiong, Q., Nano Letters 2012, 12 (8) 4305

Speaker:

Dr. A K Sinha (Centre-Director, UGC DAE Consortium for Scientific Research, Kolkata)

Title:

Manipulating Ions for Science & Technology

Date:

November 25th, 2013

Time:

04:00 pm - 05:00 pm.

Venue:

FB 382

Abstract:

We manipulate photons to form a beam of laser which finds numerous
applications. In a somewhat similar way, we manipulate fast moving
ions to use them in a very wide spectrum of scientific studies.
Many technologies emerge out of these.

I will try to cover some of the examples from my work involving such
ion manipulations. Then i will make an attempt to dwell on such ion
manipulations and their use in the Ion Beam Complex at IITK.

Speaker:

Dr. Bholanath Pahari (IISc Bangalore)

Title:

Probing Microscopic Information of Complex Materials by
Nuclear Magnetic Resonance Techniques.

Date:

November 21th, 2013

Time:

11:00 am - 12:00 noon.

Venue:

FB 382

Abstract:

Solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful physical method widely applied in modern fundamental and applied science. The two most important modes of solid state NMR for obtaining local physical and chemical information are wide-line static NMR and high-resolution magic angle spinning (MAS) NMR. Applications of both NMR modes and their advantages for the investigation of different categories of complex material will be discussed. Present seminar targets following three different topics.

1. ⁵¹V NMR studies to understand the nature of ground state and low-lying excitations in the integer spin chain (also known as Haldane chain) compound SrNi₂V₂O₈.
2. ⁷⁵As NMR for the investigation of electronic and lattice properties of recently discovered iron arsenide high-temperature superconductor CeFeAsO_1−xF_x (T_C ∼ 40 K).
3. Multinuclear MAS NMR studies to understand the structure - property relationships in oxide-ion conducting materials of P − doped La₂Mo₂O₉ .

Speaker:

Dr. Shirish Chodankar (SLS, Paul Scherrer Institut, Switzerland)

Title:

Hydration forces and ion-ion correlation in confined
fluids revealed by X-ray Reflectivity

Date:

November 18th, 2013

Time:

11:30 am - 12:30 pm.

Venue:

FB 382

Abstract:

When a liquid is confined within a nanometer-sized gap, the combination of interfacial effects and size often confer to the system properties much different from those observed in bulk fluids [1]. In particular, understanding the structure of electrolytes confined between two aluminium-phyllosilicates walls could be enlightening in a number of fields, ranging from biology to nuclear waste management, as well as clarify some fundamental issues regarding alkali hydration energies and their influence on the surrounding hydrogen bond network. We have adapted a surface force apparatus (SFA) [2] to be used as confinement device for two sets of X-ray reflectivity (XRR) experiments conducted at the cSAXS (XSA12) beamline of the Swiss Light Source at PSI. In the first set of experiments, we determined by use of XRR the distance between the surfaces and the electron density profile of the naturally present water across the hydrophilic gap at nominal zero humidity [3]. In the second set, the natural layer of K⁺ ions present on cleaved mica surfaces was substituted with monovalent Rb⁺ or divalent Sr²⁺ ions. In the third set droplets of RbCl, CsCl and BaCl₂ solutions at different concentrations were nano-confined.

We have quantitatively determined the minimum gap distance between the mica surfaces at ~ 10⁵ Pa applied pressure under the influence of different surface ions and electrolytes. In all cases we have observed layered electron density profiles within the gap, with the layering generally being stronger for more strongly correlated systems. A comparison between confined chloride solutions with different monovalent and divalent cations (Cs⁺ , Rb⁺ and Ba²⁺) reveals cation specific effects which can be related to concentration, ion size and hydration behavior. For example, we observe characteristic differences between the relative proportions of hydrated inner- and outer-sphere species and in the coverages of the inner membrane surfaces by directly adsorbed ions. Moreover, ordering in strongly correlated BaCl₂ is interpreted as alternate cation-anion layering. Structure models for the measured density profiles will be presented and discussed.
References:
1. Israelachvili, J.N., Intermolecular and surface forces: revised third edition. 2011: Academic press.
2. Perret, E., et al., Molecular liquid under nanometre confinement: density profiles underlying oscillatory forces. Journal of Physics: Condensed Matter, 2010. 22(23): p. 235102.
3. Chodankar, S., et al., Density profile of water in nanoslit. EPL (Europhysics Letters), 2012. 99(2): p. 26001.

Speaker:

Dr. Saurabh Mani Tripathi

Photonics Research Centre, Department of Computer Science and
Engineering, University of Quebec at Outaouais, Canada.

Title:

Long period grating and multimodal interference effect
based fiber-optic sensors

Date:

October 21st, 2013

Time:

3 pm - 4 pm

Venue:

FB 382

Abstract:

In this seminar I will present my resent research activities on the development of fiber-optic sensors based on (I) long-period gratings and (ii) single-multi-single (SMS) fiber optic structures. The first part
of my talk will deal with the development of bio-sensors for rapid, reliable and quantitative detection of pathogenic E. coli bacteria in water. In the second part I will discuss the role of a critical wavelength
in the performance of fiber optic devices based on modal interference. Application of modal-interference effects in bio-therapy will also be discussed.

Speaker:

A. Kani (Dept. Of Physics, IITK)

Title:

Harnessing quantum interference in atomic systems

Date:

October 7th, 2013

Time:

4 pm - 5 pm

Venue:

FB 382

Abstract:

Quantum interference between the excitation pathways modifies the optical response of the atomic system and leads to Coherent Population Trapping (CPT) and/or Electromagnetic Induced Transparency (EIT), or Electromagnetic
Induced Absorption (EIA), or Amplification without Inversion (AWI), or Enhanced Refractive Index with vanishing absorption. We will present a simple four-level atomic system interacting with a bi-chromatic light field
(double V-system) and discuss all these quantum interference effects and discuss the way to control over these effects.

Speaker:

Dr. Sayantani Bhattacharyya (Ramakrishna Mission Vivekanand University)

Title:

Detecting biomass burning emission over South East Asia from space.

Date:

September 16th, 2013

Time:

11 am - 12 am

Venue:

FB 382

Abstract:

Fluid dynamics is controlled by Navier Stokes equation. On the other hand Einstein equations control the dynamics of classical gravity. Both are complicated non linear partial differential equations with rich structure
in the space of solutions. As a consequence of AdS/CFT conjecture we expect a duality between the solutions to these two sets of equations at least in certain regime. The goal of this talk would be to explore this
duality between these two very different systems. 

Speaker:

Dr. Sourish Basu (SRON Netherlands Institute for Space Research, Utrecht, Netherlands)

Title:

Detecting biomass burning emission over South East Asia from space.

Date:

August 12th, 2013

Time:

04:00 pm - 05:00 pm.

Venue:

FB 382

Abstract:

Among the different components constituting anthropogenic CO2 emissions, biomass burning is the most uncertain. Current methods to quantify emissions from biomass burning -- such as forest fires and agricultural waste burning -- include satellite imaging to detect burnt areas and smoke plumes. However, these methods often underestimate large fire events since satellite are blind in the presence of smoke and aerosols that accompany large fires. I will describe a different -- and still developing -- method to quantify biomass burning emissions, which is to derive surface fluxes of CO and CO2 from observed gradients of those gases. Since most areas with widespread fires are devoid of surface monitoring stations, the observed gradients will be derived from satellite data. I will show how, using independent measurements of CO and CO2, we can detect fire events and quantify the amount of biomass burned.

Speaker:

Dr. Pintu Das (Institute of Physics, Goethe University – Frankfurt, Germany)

Title:

Magnetization dynamics in nano-/micro-structures using 2DEG-based micro-Hall magnetometry

Date:

August 8th, 2013

Time:

04:00 pm - 05:00 pm.

Venue:

FB 382

Abstract:

With the fast development of data storage technologies, studying the magnetization as well as domain-wall dynamics in magnetic nano- as well as micro-structures have recently found immense attention of researchers active in the field of magnetism [1]. Investigations have been carried out for arrays or assembly of magnetic particles of nanometer scale dimensions. However, measurements of assembly of particles lead to an average signal and during this process many interesting and important information get lost resulting in an incomplete understanding of the internal dynamics of individual domains or domain walls. Therefore, investigations of individual (i.e., single) magnetic entities of nano-/micron-scale dimensions are important in order to understand the magnetization process in great details. Such data can also be directly used to test the existing theories [2].
Motivated by these factors, we performed magnetic measurements of single ferromagnetic particles of micron and nano-scale dimensions using micro-Hall magnetometry method based on two-dimensional-electron-gas (2DEG) in the heterostructure of GaAs/AlGaAs. In this talk, I will discuss the results of measurements on a single CrO2 micro-crystal. With our high-sensitive measurement method, we were able to observe the transition from three-domain state to a two-domain state with a single domain-wall (separating the two domains), which was supported by micro-magnetic simulations [3]. Furthermore, we were able to track the motion of the domain wall through the sample and observed Barkhausen jumps due to the interaction with the pinning centres. Overall, the results demonstrate that micro-Hall magnetometry measurements can be used to obtain quantitative and detailed information of magnetization reversal process in individual particles of nano and micron scale dimensions. The results also allow us to estimate the density of pinning centres as a function of temperature.

References:
[1] S. Parkin et al, Science, 320, 190 (2008).
[2] K. S. Novoselov et al, Nature 426, 812 (2003).
[3] P. Das et al., Appl. Phys. Lett. 97, 042507 (2010); J. App. Phys. 112, 053921 (2012).