Speaker:

Dr. Aparna Deshpande

Affiliation:

IISER, Pune

Title:

On-surface molecular doping – a nanoscale perspective

Date:

4th Jan (Fri), 2019

Time:

11:30 AM (Tea at 11:20 AM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

Molecular assembly on a surface presents a rich testbed to probe intermolecular interactions and molecule-surface interactions. Such interactions are pertinent to understand the characteristics of the molecules and their host surfaces, which can then be tuned for applications. In this talk I will present a study of phthalocyanine (Pc) molecules on the noble metal surface - Au(111) and topological insulator surface (TI) - Bi₂Se₃ , using low temperature scanning tunneling microscopy (STM) and spectroscopy (STS). Starting with copper phthalocyanine – CuPc and its cyano analogue – CuPc(CN)8 we observe the self-assembly characterized by an organizational chirality for both these molecules on Au(111). Superimposed on this is an orbital-energy-dependent chirality seen only in the case of CuPc(CN)₈. STS measurements show an increment in the highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) gap from CuPc to CuPc(CN)₈. For Bi₂Se₃, CuPc shows a peculiar self-assembly along with single CuPc adsorption. STS measurements show a shift of the Dirac point for this system that indicates charge transfer at the molecule-TI interface. For the magnetic iron phthalocyanine – FePc, its adsorption on Bi₂Se₃ keeps the Dirac point intact indicating that the topological surface state remains protected. These findings have led to a better molecular scale picture of adsorption, self-assembly, and electronic properties along with emergent properties specific to molecule-TI hybrid interfaces.

Speaker:

Subhasish Mandal

Affiliation:

Department of Physics & Astronomy, Rutgers University, New Jersey (USA)

Title:

First principles investigation on quantum materials

Date:

24th December, 2018(Monday)

Time:

11:00 AM (tea @ 10:45AM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

Computer simulations based on first principles calculations play a central role in helping us understand, predict, and engineer physical, chemical, and electronic properties of technologically relevant materials. This can solve many problems towards building faster, smaller and cheaper devices for processing and storing information as well as for saving energy. Many of these processes involve electron excitations and strong local magnetic fluctuation that the ‘standard model’ of electronic structure, Density Functional Theory (DFT), can’t capture properly. In this context, I will highlight my work in two popular approaches that go beyond the standard DFT. Dynamical Mean Field Theory (DMFT) in combination with DFT has recently been successful for detailed modeling of the electronic structure of many complex materials with strong electron correlation. To give an example, I will show the anomalous properties of the iron-based superconductors in both bulk and monolayer phases, which have their origin in strong Hund's coupling [1]. In this context, I will discuss how computed electron-phonon coupling could be enhanced in the presence of electron correlation in FeSe. This has been recently verified in a femto-second coherent locked-in photoemission spectroscopy experiment [2,3]. Another ab-initio method that goes beyond the limit of DFT is GW-approximation, which is extensively used to compute excited states of electrons in solids. So far, most of the GW calculations have been confined to small unit-cell of bulk-like materials due to the extreme computational demand of the approach. I will discuss my collaborative effort toward developing a high scalable, open-source GW software to compute electronic excited states more efficiently for petascale architectures using the Charm++ parallel framework [4,5]. At the end, I will briefly discuss topological crystalline insulators, which are a new class of topological materials where electronic surface states are topologically protected along certain crystallographic directions by crystal symmetry. I will discuss how without any external perturbation, both massless Dirac fermions protected by the crystal symmetry and massive Dirac fermions with crystal symmetry breaking can coexist on a single surface [6].

References:

1. S. Mandal, P. Zhang, S. Ismail-Beigi, K. Haule; “How correlated is the FeSe/SrTiO3 system?”. Phys. Rev. Lett. 119, 067004 (2017).
2. S. Mandal, R. E. Cohen, and K. Haule; “Strong Pressure Dependent Electron-Phonon Coupling in FeSe”. Phys. Rev. B Rapid Communications 89, 220502(R) (2014).
3. S. Gerber et al.; “Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser” Science 357, 71 (2017).
4. M. Kim*. S. Mandal* et al. “Scalable GW software for quasiparticle properties using OpenAtom” arXiv:1810.07772 (2018).
5. http://charm.cs.illinois.edu/OpenAtom/
6. O. E. Dagdeviren*, S. Mandal* et al. Phys. Rev. Mat. 2, 114205, (2018).

Speaker:

Ashild Fredriksen

Affiliation:

Department of Physics and Technology, UiT The Arctic University of Norway

Title:

Energetic electrons near a current-free double layer in inductively coupled helicon plasma

Date:

18th December,2018(Tuesday)

Time:

4:00pm (tea @ 3:45pm)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Biosketch:

Ashild Fredriksen is a Professor in the Department of Physics and Technology at UiT The Arctic University of Norway. Her research interests include experimental plasma physics, acceleration and heating processes, current free double layers, turbulence and turbulent structures, plasma diagnostics and ion beams.

Abstract:

In inductively coupled helicon sources, current-free double layers (CFDL) can be formed self-consistently without external current forcing. The CFDLs are evidenced by an ion beam formed as a result of a potential drop between the upstream plasma source and the downstream diffusion chamber. The electrons in the double layer play an important role in balancing the ion beam current, but apart from some observations of electron energy probability functions (EEPFs) by means of Langmuir probes (K. Takahashi et al., Appl. Phys. Lett., 94, 191503 (2009)) little information has previously been obtained about the electron population in the up- and downstream regions near the CFDL.
An inverted retarding field energy analyzer (RFEA), is an ion energy analyzer biased to measure electrons instead. With this setup we measured for the first time the high-energy part of the electron distribution along the radial direction in the diffusion chamber. We found a prominent peak of high-energy electrons up to 60 eV at the footprint of the magnetic field lines emerging from the layer near the wall of the source. This coincides with increased electron temperatures and ion densities at this position. Another small but significant distribution of electrons at energies more than 100 eV are observed within the region of the ion beam itself. Later, such measurements have been performed in the source, also here with some evidence of energetic electrons.

Speaker:

Ujjal K. Dey

Affiliation:

APCTP Pohang, South Korea

Title:

Light dark matter through assisted annihilation

Date:

23rd October(Tuesday)

Time:

4:00pm (tea @ 3:45pm)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

Recent observations from direct detection experiments put stringent constraints on the popular WIMP cold dark matter (DM) models. Moreover, there are cosmological observations from the galactic scale structure formation which suggests the DM should be self-interacting and light -- the fact which is not in consonance with the WIMP paradigm. In this talk we will focus on the light dark matter scenarios where annihilation to Standard Model particles at tree-level may be kinematically forbidden. In such cases annihilation can be aided by massive Standard Model-like species, called assisters, in the initial state that enhances the available phase space opening up novel tree-level processes. We will then discuss the feasibility of such non-standard assisted annihilation processes to reproduce the observed relic density of dark matter and implications from direct detection. Finally, we shall talk about the future prospects of such DM scenarios.

Speaker:

Venkata S. Bhadram

Affiliation:

Carnegie Institute of Science, Washington D.C.

Title:

Matter under Extreme Pressures: A Route to Discover Metastable Materials

Date:

24th September, 2018

Time:

11:00 AM(Tea at 10:50 AM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

The ongoing technological advances demand the need for discovering new materials with intriguing properties. The oft-overlooked arena of metastable phases may yield promising new technological materials. [1-3] The metastable phases of materials are not the ground states at room conditions but can be accessed and stabilized using extreme environments, notably high-pressures and temperatures.[4,5] In my talk, I would present the discovery of two such metastable phases in Ti-N system, 1) TiN2, which is a promising superhard material that contains unique nitrogen subunits with highly energetic N―N single bonds [6] 2) Ti3N4, which is the first semiconducting titanium nitride known to date.[7] Although, these compounds possess positive enthalpies (thermodynamically unstable) at room conditions, high-pressure/temperature conditions made it possible to access and stabilize these phases. The strategy that we employed by marrying first principles theoretical calculations to high-pressure synthetic techniques to synthesize and characterize these materials is an unique approach towards discovering novel high-density and high-energy structures (metastable phases) of materials which are otherwise very difficult to be accessed. I would also talk about our efforts to stabilize photoresponsive solid solutions of zinc and manganese oxides in metastable rocksalt phase.[8] These phase-pure, chemically homogeneous and thermally stable (up to 500°C) novel solid-solutions exhibit moderate photocurrents when tested for solar light harvesting applications. Apart from photoresponse, these solid solutions exhibit interesting magnetic phase transition and field dependent magnetic behavior at low-temperatures.
References:
1)W. Sun et al, Science Advances, 2, 1 (2016).
2)D. Y. Kim et al, Nature Materials, 14, 169 (2015).
3)B. Keimer, J. E. Moore, Nature Physics, 13, 1045 (2017).
4)V. V. Brazhkin, “High-Pressure Synthesized Materials: Treasures and Hints” High Pressure Research, 27, 333 (2007).
5)W. Sun et al, Thermodynamic Routes to Novel Metastable Nitrogen-Rich Nitrides, Chemistry of Materials, 29, 6936 (2017).
6)V. S. Bhadram, D. Y. Kim and T. A. Strobel. “High-Pressure Synthesis and Characterization of Titanium Pernitride.” Chemistry of Materials, 28, 1616 (2016).
7)V. S. Bhadram, H. Liu, E. Xu, T. Li, T. A. Strobel, “Semiconducting Cubic Titanium Nitride in the Th3P4 structure.” Physical Review Materials, 2, 011602 (R) (2018).
8)V. S. Bhadram, Q. Cheng, C. K. Chan, Y. Liu, K. Landskron, and T. A. Strobel, “ZnxMn1-xO Solid Solutions in the Rocksalt Structure: Optical, Charge-Transport and Photoelectrochemical Properties. ACS Applied Energy Materials, 1, 260 (2018).

Speaker:

Dr. K.R. Koteswara

Affiliation:

Technische Universitaet Dortmund, Germany

Title:

Quantum Information Processing and Hyperpolarization of nuclear spins using Nitrogen-Vacancy centers in diamond

Date:

13th September, 2018

Time:

11:00 AM(Tea at 10:50 AM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

Nitrogen-Vacancy (NV) centers in diamond have interesting properties for a number of quantum technologiesincluding quantum information processing and nano-scale Nuclear Magnetic Resonance (NMR). In this presentation, I will talk about our recent experimental research on NV centers for the applications of quantum information processing and hyperpolarization of nuclear spins.I will first introduce NV centers, their properties and some of their applications. Then, I will talk about interactions between single electron spins of NV centers and proximal nuclear spins and interesting level anti-crossings that occur because of these interactions. Some of the interesting results of this analysis are (i) dynamics of a single-spin driven beyond the rotating-wave approximation and (ii) decoherence-free subspaces. Next, I will talk about transferring polarization of optically pumped NV centers to bulk 13C nuclear spins of the diamond lattice. Finally, I will discuss strategies to realize scalable quantum information processing using NV centers and transferring polarization of optically pumped NV centers to nuclear spins outside the diamond surface.

Speaker:

Ish Dhand

Affiliation:

Ulm University, Ulm, Germany

Title:

Proposal for Quantum Simulation via All-Optically Generated Tensor Network States

Date:

4th September, 2018

Time:

04:00 PM(Tea at 3:45 PM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

We devise an all-optical scheme for the generation of entangled multimode photonic states encoded in temporal modes of light. The scheme employs a nonlinear down-conversion process in an optical loop to generate one- and higher-dimensional tensor network states of light. We illustrate the principle with the generation of two different classes of entangled tensor network states and report on a variational algorithm to simulate the ground-state physics of many-body systems. We demonstrate that state-of-the-art optical devices are capable of determining the ground-state properties of the spin-1/2 Heisenberg model. Finally, implementations of the scheme are demonstrated to be robust against realistic losses and mode mismatch.

Speaker:

Dr. Vishwanath Shukla

Affiliation:

Post-Doc, L'Institut de Physique de Nice (INPHYNI), Université Côte d’Azur, Nice, France.

Title:

Collisions of active particles in quantum fluids and quantitative estimation of effective viscosity in quantum turbulence

Date:

30th August, 2018

Time:

04:00 PM(Tea at 3:45 PM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

Particles of low velocity, traveling without dissipation in a superfluid, can interact and emit sound when they collide. We propose a minimal model in which the equations of motion of the particles, including a short-range repulsive force, are self-consistently coupled with the Gross-Pitaevskii equation. We use this model to demonstrate the existence of an effective superfluid-mediated attractive interaction between the particles; and we study numerically the collisional dynamics of particles as a function of their incident kinetic energy and the length-scale of the repulsive force. We find a transition from almost elastic to completely inelastic (sticking) collisions as the parameters are tuned. We find that aggregation and clustering result from this sticking transition in multi-particle systems. We also report our recent results on the decay of three-dimensional quantum turbulence at finite temperatures and provide a quantitative estimation of effective viscosity at finite temperatures.

Speaker:

Dr. Sourabh Lahiri

Affiliation:

BIT Mesra, Ranchi

Title:

Some aspects of Stochastic Thermodynamics and Quantum Random Walk

Date:

27th August, 2018

Time:

04:00 PM(Tea at 3:45 PM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

The talk would be divided into two parts. In the first half, I will provide a pedagogical introduction to Stochastic Thermodynamics (i.e., Thermodynamics applicable to systems at mesoscopic scales), followed by stating a few results that we have contributed to. The second half would involve the description of a quantum particle evolving under tight-binding Hamiltonian on a one-dimensional lattice having a detector at the origin. A method of computing the survival probability and the first detection time probability would be discussed.

Speaker:

Sathyanarayana Paladugu

Affiliation:

Kent State University

Title:

Tunable Electrophoresis of Colloids in Liquid Crystalline Electrolytes

Date:

23th August, 2018

Time:

11:00 AM (Tea at 10:50 AM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

Electokinetics in colloidal systems represents a broad and interesting class of out-of-equilibrium effects, caused by the external electric field that acts on spatially separated charges. Usually, the colloids are dispersed in an isotropic electrolyte such as water. In this seminar, first we discuss about many-body effects for the critical Casimir forces emerging in the presence of several colloidal particles within a critical mixture of water and 2,6-lutidine. Critical Casimir forces emerge on objects immersed in binary liquid mixtures kept near their critical (demixing) points due to the confinement of the spatial fluctuation of the local mixture composition. By taking advantage of a spatial light modulator (SLM), we generate multiple reconfigurable holographic optical tweezers (HOTs) which permit to optically trap several colloids. The forces acting on them are then determined via digital video microscopy. We first study the critical Casimir force arising between two particles as a function of their distance and then we investigate how this is affected by the presence of a third neighbouring particle. Later we discuss novel features of the dynamic out-of-equilibrium behavior of colloids when the disperse medium is an anisotropic electrolyte, namely, a nematic liquid crystal. Because of orientational order, nematics show anisotropy of properties such as electric conductivity and dielectric permittivity. When the electric field is applied to a nematic with a director that varies in space, anisotropy causes the ionic charges to separate in space. The density of space charge is proportional to the applied field, director gradients, anisotropy of conductivity and permittivity. In other words, separation of charges is defined by the properties of the liquid crystal electrolyte rather than by the properties of the solid component as in the case of isotropic electrolytes. The separated charges move in the electric field, creating electro-osmotic or electrophoretic effects with velocities proportional to the square of the electric field. We use nematic cells with photopatterned director field to illustrate the principle of the liquid crystal-enabled electrokinetics and its advantages, such as steady character of flows, control of vorticity, and the ability to transport colloidal particles of any type (solid, liquid, gaseous). We also demonstrate that the colloidal particles can be electrophoretically active even in a uniform nematic cell, provided their surface induces local dipole-like director distortions. Such a particle will move even if the electric conductivity is isotropic, being supported solely by the dielectric anisotropy. We demonstrate that the change in the sign of anisotropy causes reversal of the particle motion. Finally, we also demonstrate that the electric field can produce particle-like propagating solitary waves representing self-trapped “bullets” of oscillating molecular director. These director bullets lack fore-aft symmetry and move with very high speed perpendicularly to the electric field and to the initial alignment direction. The bullets are true solitons that preserve spatially confined shapes and survive collisions.

Speaker:

Dr. Juzar Thingna

Affiliation:

University of Luxembourg, Luxembourg

Title:

Nonequilibrium statistical physics: A master equation perspective

Date:

20th August, 2018

Time:

04:00 PM (Tea at 3:45 PM)

Venue:

FB 382(Prof. Amal Raychaudhuri Seminar Room)

Abstract:

I will give in this talk a basic overview of the key concepts in nonequilibrium statistical physics and its connections to the theory of classical and quantum open systems described via master equations. In the first part of the talk, I’ll discuss the basics of the theory of open systems and its historical sources that can be traced back to Pauli (1928), Lindblad (1976), and others. I’ll also describe the thermodynamic framework that forms a super structure on the master equations and can be applied to systems in equilibrium and nonequilibrium. In the second part, I will briefly talk about some of the recent advances in the theory of open systems, taking three examples: i. Beyond weak system-reservoir coupling, ii. Large synchronizing networks, and iii. Finite reservoirs, and its consequences on the nonequilibrium thermodynamics.

Speaker:

Dr. Jayita Nayak

Affiliation:

University of California Davis, USA

Title:

Electronic structure of topological materials and quasicrystals

Date:

7th August (Tuesday), 2018

Time:

11:00 AM (Tea at 10:50 AM)

Venue:

FB 382(Prof. Amal Raychaudhuri seminar room)

Abstract:

The discovery of topological materials has created tremendous attention in the scientific community and beyond because these materials can exhibit a novel state of matter in which topologically protected gapless states on their edges or surfaces are present. Such states are protected from scattering by impurities and thus have important technological applications. The rare-earth monopnictide LaBi, LaSb exhibits very large, unusual magnetoresistance which stimulates the interest in directly observing any topological surface states. Although band inversions have been postulated to induce a topological phase in LaBi but there was no experimental evidence for topological surface states in this compound. By using angle-resolved photoemission spectroscopy (ARPES) and ab-initio calculations, we have revealed the existence of topological surface states of LaBi through the observation of three Dirac cones: two coexist at the corners and one appears at the centre of the Brillouin zone. The odd number of surface Dirac cones is a direct proof of the topological nature of LaBi compound. Moreover, our ARPES measurement in conjugation with band structure calculation established the Type II Dirac semi metallic phase in PtSe2. In my recent work, six fold degeneracy has been observed at the crossing point in PdSb2 compound in contrast to Dirac and Weyl semimetals. We have used hard x-ray photoelectron spectroscopy (HAXPES) to investigate the bulk electronic structure of quasicrystals to resolve the controversy about the existence of pseudogap in these materials. The near Fermi edge (EF) spectra of Al-Pd-Mn as well as Al-Cu-Fe are strongly suppressed in intensity at EF, which provides strong evidence for the existence of the pseudogap in contrast to surface sensitive low energy photoemission spectra that shows a metallic Fermi edge. From fitting of the spectra by inverted Lorenzian function the evidence of fully formed pseudogap in Al-Cu-Fe demonstrate that the DOS at EF is zero indicating that it is close to a metal-insulator phase boundary. The existence of deeper pseudogap in bulk has been supported by the theoretical calculations. On the other hand, the HAXPES near EF spectrum of both Zn-Mg-Dy and Zn-Mg-Y exhibits shallower pseudogap compared to the Al based quasicrystals (Al-Pd-Mn and Al-Cu-Fe) that may be related to their larger carrier concentration compared to Al-Pd-Mn.

Speaker:

Dr. Debabrata Mishra

Affiliation:

Department of Physics & Astrophysics, University of Delhi

Title:

General Physics Seminar: Chirality Induced spin selectivity in electron transmission through self-assembled monolayers of biomolecules and its applications

Date:

29th September (Thursday), 2016

Time:

2:30 PM

Venue:

FB 382

Abstract:

In a ground breaking discovery at Weizmann Institute of Science, we have found that electrons, transmitted through helical (chiral) protein, DNA and peptides, yield spin polarized electron (up to 64% for DNA) due to the lack of inversion symmetry associated with the chiral (DNA) molecules. ‘Chirality’ in molecular systems represents structural asymmetry in which one enantiomer has “right handed” symmetry and the other “left handed”. The interaction of circularly polarized light, magnetic field or spin-polarized electrons with this chiral potential varies for the specific enantiomer and gives exciting results. I will present the discovery and development of chirality induced spin selectivity effect of self-assembled monolayers made from molecules having a helical structure, like protein (bacteriorhodopsin), dsDNA and oligopeptides of different molecular length adsorbed on Au, Ni and Al thin films. Our results indicate that helical structure promotes electron transmission and efficient spin filtering at room temperature. Interestingly, this effect could be exploited to see the spin dependent photoluminescence behavior induced by chiral protein in a hybrid semiconductor quantum dot-Protein thin film. I will also briefly discuss on some of the exciting results on spin specific chemical reactions induced by chiral dsDNA and my future research plan.

Speaker:

Professor Sanjoy Biswas

Affiliation:

Korea Institute for Advance Study

Title:

General Physics Seminar: Closing in on the Standard Model like Higgs boson

Date:

1st March (Tuesday)

Time:

4:00 PM

Venue:

FB 382

Abstract:

The Large Hadron Collider Experiment at the CERN has discovered a Higgs-like resonance. However, the confirmation of any resemblance with the Standard Model Higgs boson requires a precise measurements of its properties and couplings with the Standard Model particles. In addition, it is also important to look for any hint of New Physics that might be associated with its production and/or decay. In this talk, I will shed some light on some of these issues.

Speaker:

Dr. Tanmoy Mondal

Title:

Vacuum stability and unitarity in Left-Right Symmetric Model

Date:

25th Feb, 2016

Time:

3:00 PM

Venue:

FB 382

Abstract:

Left-Right symmetric models are very appealing as BSM scenarios. In this talk I will discuss how theoretical constrains can be useful to restrict the LR model. Using copositivity we computed the criteria which guarantee that the vacuum is bounded from below in all directions. We examine the usefulness of the unitarity conditions which can translate into giving a stronger constraint on the model parameters together with the criteria derived from vacuum stability and perturbativity. In this light, we demonstrate the bounds on the masses of the physical scalars present in the model and find the scenario where multiple scalar modes are in the reach of Large Hadron Collider.

Speaker:

Professor Sei Suzuki

Affiliation:

Department of Liberal Arts Saitama Medical University Moroyama, Saitama 350-0495, Japan

Title:

Dynamics of decoherence of a qubit coupled to a spin-chain environment

Date:

24th Feb, 2016

Time:

3:00 PM

Venue:

FB 382

Abstract:

Decoherence of a quantum system is one of the important issues in quantum computation and quantum information. Controlling decoherence has been discussed recently in NMR or cold atomic experiments. We study the time dependence of the decoherence of a single spin interacting with a spin-chain environment. When the environment is close to a quantum critical point, the decoherence of a system may show a time dependence characteristic to the universality of the associated quantum critical point. In the seminar, we shall present a universal scaling theory of decoherence of a single spin when the system-environment coupling is week and the environment is slowly varied with time across a quantum critical point.

Speaker:

Mr. Atanu Rajak

Affiliation:

Saha Institute of Nuclear Physics, Kolkata

Title:

Statics and dynamics of topologically ordered and quenched disordered quantum many body systems

Date:

25th February 2016 (Thursday)

Time:

4:00 PM ( Tea will be served at 3:45 PM)

Venue:

FB 382

Abstract:

Given the recent interest in the non-equilibrium quenching dynamics of quantum many-body systems across quantum critical points (QCPs), the studies involving quenching dynamics of a topological system across a QCP have emerged as a rapidly growing field of research. Especially, the quenching dynamics of a topological insulator and the p-wave superconductors have been explored in this connection. In the first part of this talk, I will discuss the dynamics of a Majorana edge mode in a p-wave superconducting chain following sudden and slow changes of a parameter of the Hamiltonian across QCPs. The survival probability of an edge Majorana as a function of time is studied when the system is suddenly driven from one topological phase to the other and also to the QCPs separating these phases. In the context of slow quenching dynamics of a finite p-wave superconducting chain with a complex hopping term, we ask the question whether an edge Majorana can be transported from one topological phase to the other across a gapless region. While an extensively studied NP-hard search problem of the ground state is that of the Sherrington-Kirkpatrick (SK) model. In the next part, I will speak on an interesting result that the crossover between classical (thermal) and quantum fluctuation dominated critical behaviors for the SK spin glass in transverse field occurs at a non-vanishing temperature.

Speaker:

Professor Janusz Gluza

Affiliation:

Institute of Physics, Katowice Poland

Title:

High Energy Physics Seminar: Techniques and tools for loop calculations. Mellin-Barnes integrals, the AMBRE package

Date:

22. 02. 2016 ( Monday)

Time:

4:00 PM ( Tea will be served at 3:45 PM)

Venue:

FB 382

Abstract:

I will shortly summarize methods and software used in precise multi-loop calculations. Then I will discuss pros and cons of the Mellin-Barnes method. I will demonstrate on a couple of running examples how to use the Mathematica package AMBRE/MB (for the files see: http://prac.us.edu.pl/~gluza/ambre/).

Speaker:

Dr. Mayukh Ray

Affiliation:

Saha Institute of Nuclear Physics, Kolkata

Title:

CONDENSED MATTER PHYSICS SEMINAR: Influence of Martensite Transformation on the Magnetic and Transport Properties of Ni-Mn based Heusler Alloys

Date:

9th February, 2016 (Tuesday)

Time:

11:00 AM, Tea at 10:50 AM

Venue:

FB 382 (Physics Seminar Room)

Abstract:

The striking applicable properties and complex magnetism of Ni-Mn based Heusler alloys are mainly arises due to the first order martensite transformation (MT). Thus, it is necessary to understand the influencing factors [1]. The magnetic ground state of this dense magnetic type system giving rise to cluster spins glass state apart from its re-entrant spin glass behaviour. We will discuss it on the context of d.c and a.c magnetization and low temperature specific heat measurements [2]. The high field cooling through the irreversibility temperature finds more significant effect on the thermo-remanent magnetization (TRM) of martensite phase than the system cooled only through its martensite transformation (MT) [3]. This observation cannot be explained using the theory of kinetic arrest for first order transition. How one can induce a ferromagnetic austenite phase in place of paramagnetic austenite phase without altering the magnetic behaviour of low temperature martensite phase. I will also discuss how the martensite and austenite phase fraction across the MT influence the magneto-resistance when a magnetic field is applied. The origin of giant magneto-resistance across the MT will also be discussed [4]. References 1. Ray et al. J. Appl. Phys. 114, 123904 (2013). 2. Ray et al. Euro. Phys. Lett. 109, 47006 (2015). 3. Ray et al. J. Magn. Magn. Mater. 396, 26 (2015). 4. Ray et al. J. Phys. D: Appl. Phys. 47, 385001 (2014).

Speaker:

Dr. K. S. Narain

Affiliation:

Abdus Salam International Center for Theoretical Physics, ASICTP, Trieste, Italy

Title:

High Energy Physics Seminar : Physical string realization of Walcher's Topological string

Date:

08. 02. 2016 (Monday)

Time:

4:00 PM ( Tea will be served at 3:45 PM)

Venue:

FB 382

Speaker:

Dr. U. Chandni

Affiliation:

California Institute of Technology, USA

Title:

General Physics Seminar: Engineering quantum transport in low dimensional electron systems

Date:

1st February (Monday) 2016

Time:

11:0 AM, Tea at 10:50 PM

Venue:

FB 382 (Physics Seminar Room)

Abstract:

When electron systems are constrained to low dimensions, interactions can lead to exciting many body physics and broken symmetry states, exhibiting topological order and emergent behavior. In this talk, I will discuss electron transport in nanoscale structures consisting of two dimensional (2D) layered materials as well as one dimensional metallic nanowires. Firstly, I will discuss our efforts to engineer spin-orbit effects in graphene. This was spurred by recent theoretical predictions that heavy metal adatoms such as Indium can introduce spin-orbit coupling in graphene and lead to topological states of matter. In the second part of the talk, I will discuss our ongoing efforts in understanding electron tunneling in Van der Waals heterostructures. We employ atomically thin layers of hexagonal boron nitride as the insulating layer and metals or graphite/graphene as the counter-electrodes. Our results show strong evidence for phonon and defect mediated tunneling in such heterostructures. I will also briefly describe some of our earlier experiments on transport in ultrathin gold nanowires. We observe tunability between a non-Fermi Luttinger liquid state and a disordered state exhibiting hopping transport. In the end, I will present how these efforts can be expanded to create heterostructures of 1D and 2D materials to further explore spintronics, straintronics, tunneling and spin-orbit interactions among other phenomena.

Speaker:

Dr. Ishan Talukdar

Affiliation:

University of California, Berkley CA, USA

Title:

Trapped ions for quantum information processing

Date:

1 February, 2015

Time:

4:00 PM (Tea at 3.45 pm)

Venue:

FB 382 (Physics conference room)

Abstract:

Laser-cooled and electromagnetically confined ions offer a quantum information processing platform with a great degree of coherence and tunability. In order to utilize such a system to solve classically hard problems, scaling to a larger computational manifold is necessary. Microfabricated surface traps promise scalability, however bringing along a new set of challenges. In this talk, after an introduction to this technology, I will discuss our efforts in understanding and tackling a source of anomalous noise in surface traps which can compromise fidelities of quantum gate operations.

Speaker:

Dr. Ketan Patel

Affiliation:

IISER Mohali

Title:

Anarchic Yukawas in Higher Dimensional Theories

Date:

28th January (Thursday)

Time:

4 pm

Venue:

FB 382

Abstract:

Can very special pattern of fermion masses be obtained without a symmetry principle? I will try to address this question in a higher spacetime dimensional framework. An extra-dimension compactified on an orbifold generates different zero-mode profiles for fermions of different charges. Utilizing suitable scalar fields, a predictive model for fermion masses and mixing is constructed and shown to be viable with the current data. All the Yukawa couplings in the model are of order unity while the hierarchies among different fermions result from the wave-function profiles. The naturalness of anarchical Yukawa couplings and predictions for various experimentally observable parameters will be discussed.

Speaker:

Dr. Kush Saha

Affiliation:

University of California, Irvine

Title:

TPSC Seminar series: Interplay between electronic band topology and phonons in Dirac materials

Date:

11th January, 2016 (Monday)

Time:

4-5 PM (Tea 3.45 PM onwards)

Venue:

FB 382

Abstract:

In this talk, I will discuss topological phase transition in intrinsically nontopological materials. In particular, I will show that electron-phonon interactions can induce topological phases in direct and narrow-gap Dirac insulators. The underlying mechanism for this effect can be explained in terms of the electron-phonon scattering matrix elements, which show a peculiar dependence on the sign of the mass of the Dirac fermions. A similar mechanism applies to weak Coulomb interactions and spin-independent disorder; however, the influence of these on band topology is largely independent of temperature. Finally, I will discuss the inverse of the above effect, concerning back action of the electronic band topology on the phonons. In particular, I will show that phonon linewidth may help detect the topology of the electronic bands. The underlying mechanism can again be attributed to the electron-phonon matrix elements as mentioned before.

Speaker:

Dr. Samir Kumar Biswas

Affiliation:

IIT, Hyderabad

Title:

Developing opto-acoustic based diagnostic devices: theory, design, optimization and patient measurement

Date:

11th January, 2016 (Monday)

Time:

4 pm

Venue:

SL215 (CELP seminar room)

Abstract:

Light and ultrasound transport through living tissue has been the focus of recent research in biophysics and bioengineering, mainly due to its potential application in non-destructive non-invasive diagnostic pathology. Using soft radiation like light and ultrasound, the tissue activities such as metabolism, blood flow in tissue can be quantified by correlating them with chromophores (haemoglobin, melanin, water, lipid etc). My talk will be the physics of soft matter under non-ionized radiation for tissue parameter extraction where light-tissue and ultrasound-tissue interaction will be modelled with second order partial differential equation. With advanced mathematics, physics of light and acoustic, the angiogenesis in human subjects and rat brain over a virtual domain will be reconstructed to understand the neurological problem, inflammation, arthritis progress in human inflamed joints and other possibilities such as melanoma in skin, lymph nodes inflammation etc will be the matter of discussion.

Speaker:

D.Venkateswarlu

Affiliation:

UGC-DAE Consortium for Scientific Research, Indore

Title:

Superconductivity in Oxy-nitrides and Skutterudites

Date:

6th January 2016 (Wednesday)

Time:

11 am

Venue:

FB-382

Abstract:

Resistive broadening of Niobium Oxy-nitride samples is studied in terms of Aslamazov and Larkin (AL) theory &Lowest Landau Level (LLL) scaling for data collected down to 2K and fields upto 14T. The fluctuation dimensionality of the system is estimated from the analysis apart from other interesting parameters of interest like Ginzburg number, coherence length etc. The magnetic field induced broadening has been analysed in the TAFF (Thermally Activated Flux Flow) formalism. The activation energies of flux linesare obtained that shows a collective pinning scenario at higher magnetic fields. At low temperatures and high enough magnetic fields, a vortex glass state is observed in Niobium Oxy-nitride samples and the relevant parameters of interest are discussed. Skutterudites are relatively a new family of thermoelectric materials having promising thermoelectric properties especially due to the rattling like motion of filler atoms. The ground state of such materials is quite interesting as many of them are quite unconventional. Superconductivity in these systems is so because of the interplay between pairing and magnetism in these materials. A case study of PrPt4Ge12shows that there is a survival and existence of superconducting energy gap even after the removal of Pr down to 50 at % in PrPt4Ge12, that prelude the existence of superconductivity in an otherwise Pt4Ge12 cage as predicted by theory. Pr acts as the main stabilizing agent. A point-nodal to node-less evolution of superconducting energy gap is shown to exist as a function of Nd co-doping with Pr (up to 0.3) in Pr1-xNdxPt4Ge12 using heat capacity.

Speaker:

Dr Arun M. Thalapillil

Affiliation:

Department of Physics and Astronomy Rutgers, The State University of New Jersey

Title:

Probing New Physics at the LHC, Future Colliders & Yonder…

Date:

5th January (Tuesday) 2016

Time:

4 PM

Venue:

FB-382

Abstract:

The discovery of the Higgs boson has opened up new avenues to probe for physics beyond the standard model, and motivates us to revisit aspects of various models in this new light. In this talk I would like to briefly discuss three topics influenced by this - searches at the LHC & future PP-colliders for SM gauge singlet states that couple to the Higgs; supersymmetric, radiatively-generated fermion masses in the context of Higgs-fermion couplings and the muon anomalous magnetic moment; and lastly, flavor constraints on extended gauge mediation models, that accommodate large A-terms.

Speaker:

Dr Arun M. Thalapillil

Affiliation:

Department of Physics and Astronomy Rutgers, The State University of New Jersey

Title:

Here be Dragons - The Coming Era of Discovery at the LHC & Beyond…

Date:

4th January (Monday) 2016

Time:

4 PM

Venue:

FB-382

Abstract:

A new era has already begun with the advent of the Large Hadron Collider (LHC). Other collider and non-collider experiments, either currently running or planned for the near future, promise to shed light on some of the most intriguing questions in physics today - are there new symmetries of nature, what comprises dark matter, why is there a matter anti-matter asymmetry, what is the origin of fermion masses and so on. The Higgs boson, an excitation of the field responsible for electroweak symmetry breaking and the origin of mass, has already been discovered. A similar era of investigation into uncharted territory, at the frontier, has not existed in many decades! In this talk, I would like to briefly discuss how some of the experimental discoveries and programs specifically relating to the Higgs-like resonance have opened up new avenues, to probe and think about new physics.

Speaker:

Dr. Pradipta Ghosh

Affiliation:

Laboratoire de Physique Théorique, Orsay Université de Paris-Sud

Title:

Light singlets in supersymmetry: A glimpse beyond the Standard Model

Date:

15th December, Tuesday

Time:

4 PM

Venue:

FB-382

Abstract:

Supersymmetry is a well-motivated extension beyond the standard model to overpower its shortcomings. Certain supersymmetric models contain non-minimal field content. These models can easily accommodate light neutral scalar(s) and fermion(s) in the spectrum. These light states have different novel phenomenological implications, e.g., producing unusual decay modes for the heavier standard model particles, like W ± , Z and Higgs. An analysis of this kind is a viable alternative to probe physics beyond the standard model even when rest of the mass spectrum remains beyond the reach of the LHC. We exemplify our analysis for two non-minimal supersymmetric models with singlet superfields.

Speaker:

Dr. Pradipta Ghosh

Affiliation:

Laboratoire de Physique Théorique, Orsay, France

Title:

When Neutrinos meet the Collider

Date:

10th December (Thursday)

Time:

3:30 PM

Venue:

FB-382

Abstract:

Experimental detection of neutrino oscillation provides firm evidence of physics beyond the standard model. Some of these new theories predict intriguing correlations between a few collider observables and the neutrino mixing angles. Measurements of these collider observables are highly envisaged during run-II of the LHC with upgraded configurations. We investigate complementary aspects of the collider and neutrino physics experiments through these correlations. We show how one can utilise these correlations to discriminate different new physics scenario.

Speaker:

Dr. Arijit Kundu

Affiliation:

Technion, Israel

Title:

Non-trivial Transport in Floquet Topological Insulators

Date:

26th November 2015 (Thursday)

Time:

4.00 PM

Venue:

FB-382

Abstract:

Floquet topological insulators are characterized by invariant, called Bott indices, which have no equilibrium analogue. Systems with non-vanishing Bott indices may give rise to counter-intuitive transport phenomena, especially in a disordered system. For instance, the disorder can enhance the transport, in presence of certain lattice symmetry. Whereas, in certain highly disordered Floquet topological insulator, quantized charge transport can take place through edge states, where the bulk behaves as an Anderson insulator.

Speaker:

Dr. Arijit Kundu

Affiliation:

Technion, Israel

Title:

Topology and Transport in Periodically Driven Systems

Date:

24th November 2015 (Tuesday)

Time:

4.00 PM

Venue:

FB-382

Abstract:

Topological systems in condensed matter are characterized by quantities which can only be measured non-locally. One way to introduce topological phases in certain systems is periodic driving. For example, an 1D p-wave superconductor, when driven periodically, becomes topologically non-trivial and hosts exotic steady states, which are called Floquet Majorana fermions. Whereas, graphene, under the application of circularly polarized laser is an example of Floquet topological insulator. Such topological insulators, like the quantum-hall systems, have non-trivial topology and chiral edge states which give rise to novel transport characteristics which are unique to the time-periodic systems. These systems present potential applications to various fields from quantum computation to valleytronics.

Speaker:

Dr. Panchanana Khuntia

Affiliation:

Laboratoire de Physique des Solides, Universit´e Paris-Sud 11, UMR CNRS, 91405 Orsay, France

Title:

NMR as a Local Probe for Magnetism and Spin Dynamics

Date:

5th October 2015 (Monday)

Time:

10:00 a.m.-11:00 a.m.

Venue:

FB-382

Abstract:

I will give a brief overview of Nuclear Magnetic Resonance (NMR) and the capability of this tool in uncovering the underlying mechanism for the emergent physical phenomena such as unconventional superconductivity and phase transitions on a microscopic scale in strongly correlated electron systems. I will also present our recent results on a new frustrated quantum magnet with exotic magnetic properties. Most of the physical phenomena in correlated electron materials often elude standard theoretical paradigms, even though the properties of the individual particles that constitute these materials are well established. In many cases, understanding the novel phases and establishing a suitable model in interacting quantum systems is still an unsettled issue, which signals the frontiers of our knowledge in this field. The development of modern material synthesis method, state art of the experimental techniques, and advances in theory have reinvigorated opportunities for investigating emergent properties of quantum materials. These materials might serve as model materials for hosting exotic excitations pertinent to novel states and to test theoretical conjectures [1,2,3]. Our recent comprehensive investigation demonstrates the role of persistent spin dynamics down to T→0 induced by frustration in stabilizing the exotic spin liquid state in a novel S = 1/2 frustrated quantum magnet [4]. References [1] P. Khuntia et al., Phys. Rev. Lett. 113, 216403 (2014). [2] P. Khuntia et al., Phys. Rev. B 86, 220401(R) (2012). [3] A. K. Nayak et al., Nature Materials, 14, 679 (2015). [4] P. Khuntia et al., (submitted to Phys. Rev. Lett.).

Speaker:

Jyotirmoy Bhattacharya

Affiliation:

Department of Mathematical Sciences, Durham University, UK.

Title:

Constraints on hydrodynamic transport phenomena from equilibrium partition functions.

Date:

23rd September 2015 (Wednesday)

Time:

4 PM

Venue:

FB-382

Abstract:

We will discuss the equilibrium thermal partition function for quantum field theories on arbitrary stationary background spacetime, in the long wavelength expansion. We shall first consider space-filling fluids and demonstrate that the equations of relativistic hydrodynamics are significantly constrained by the requirement of consistency with such a partition function. In this case, these constraints coincide precisely with the relations between transport coefficients that follow from the second law of thermodynamics. We will then use the power of this partition function formalism, to study and constrain the surface transport properties of fluids.

Speaker:

Jyotirmoy Bhattacharya

Affiliation:

Department of Mathematical Sciences, Durham University, UK.

Title:

Geometric aspects of quantum entanglement

Date:

22nd September 2015 (Tuesday)

Time:

4 PM

Venue:

FB-382

Abstract:

We shall begin with a brief introduction to the basic concepts behind the gauge-gravity duality. In this context, we will go on to describe how the notion of entanglement entropy in quantum field theory, acquires a geometrical interpretation. Using such geometric techniques, we will explore some interesting properties of entanglement entropy, which has close resemblance with thermodynamics laws. We will then speculate on how these properties may be helpful to recast gravitational dynamics as an effective dynamics of quantum entanglement, via the gague-gravity duality

Speaker:

Hilal Ahmed

Affiliation:

AMU, Aligarh

Title:

Synthesis and Characterization of Nanocrystalline Colossal
Magnetoresistive Manganites

Date:

13th February 2015 (Friday)

Time:

11 am

Venue:

FB-382

Abstract:

In this talk, I shall present results obtained on nanocrystalline Sr-doped LaMnO₃. The parent material LaMnO₃ is an antiferromagnetic insulator at room temperature. Strontium (Sr) doped LaMnO3 is an interesting manganite which shows ferromagnetism at room temperature with a rich phase diagram. These materials are well suited for spintronics and biomedical applications

Speaker:

Hilal Ahmed

Affiliation:

AMU, Aligarh

Title:

Synthesis and Characterization of Nanocrystalline Colossal
Magnetoresistive Manganites

Date:

13th February 2015 (Friday)

Time:

11 am

Venue:

FB-382

Abstract:

In this talk, I shall present results obtained on nanocrystalline Sr-doped LaMnO₃. The parent material LaMnO₃ is an antiferromagnetic insulator at room temperature. Strontium (Sr) doped LaMnO3 is an interesting manganite which shows ferromagnetism at room temperature with a rich phase diagram. These materials are well suited for spintronics and biomedical applications

Speaker:

Hilal Ahmed

Affiliation:

AMU, Aligarh

Title:

Synthesis and Characterization of Nanocrystalline Colossal
Magnetoresistive Manganites

Date:

13th February 2015 (Friday)

Time:

11 am

Venue:

FB-382

Abstract:

In this talk, I shall present results obtained on nanocrystalline Sr-doped LaMnO₃. The parent material LaMnO₃ is an antiferromagnetic insulator at room temperature. Strontium (Sr) doped LaMnO3 is an interesting manganite which shows ferromagnetism at room temperature with a rich phase diagram. These materials are well suited for spintronics and biomedical applications

Speaker:

Hilal Ahmed

Affiliation:

AMU, Aligarh

Title:

Synthesis and Characterization of Nanocrystalline Colossal
Magnetoresistive Manganites

Date:

13th February 2015 (Friday)

Time:

11 am

Venue:

FB-382

Abstract:

In this talk, I shall present results obtained on nanocrystalline Sr-doped LaMnO₃. The parent material LaMnO₃ is an antiferromagnetic insulator at room temperature. Strontium (Sr) doped LaMnO3 is an interesting manganite which shows ferromagnetism at room temperature with a rich phase diagram. These materials are well suited for spintronics and biomedical applications

Speaker:

Hilal Ahmed

Affiliation:

AMU, Aligarh

Title:

Synthesis and Characterization of Nanocrystalline Colossal
Magnetoresistive Manganites

Date:

13th February 2015 (Friday)

Time:

11 am

Venue:

FB-382

Abstract:

In this talk, I shall present results obtained on nanocrystalline Sr-doped LaMnO₃. The parent material LaMnO₃ is an antiferromagnetic insulator at room temperature. Strontium (Sr) doped LaMnO3 is an interesting manganite which shows ferromagnetism at room temperature with a rich phase diagram. These materials are well suited for spintronics and biomedical applications

Speaker:

Prof. A. P. Baburaj

Affiliation:

IIT Madras

Title:

The boundary layer velocity field in turbulent convection

Date:

25th April, 2015 (Saturday)

Time:

11 am

Venue:

Old core lab 103E

Abstract:

We measure the spatial velocity field in a horizontal plane within the velocity boundary layer over the horizontal hot plate in turbulent convection in water for 105 Ra 109 and Pr around 5. A new criterion is used to detect the coherent structures, namely line plumes, from this velocity field. The velocity field mostly shows four types of flow patterns, we present the PDF of velocities for each patterns to show their differences. The instantaneous velocity distributions match with that of laminar natural convection boundary layers, with the regions far away from plumes being affected by the external shear at the larger Ra. The mean velocity fields show no clear patterns and the fluctuating velocity fields show velocity field devoid of the mean shear, i.e. the pattern of flow driven by the plumes alone. The PDF of velocities of the plumes and the fluctuating components of the flow velocities coincide implying that plumes mostly contribute to the fluctuating velocity field. The joint PDF of horizontal and vertical instantaneous velocities show an 'arrow' type structure with the arms of the arrow head showing plume and boundary layers while the arrow shaft showing shear affected regions. The spectra of instantaneous velocities show a Bolgiano-Obukhov scaling at larger wave numbers while it shows a -1 scaling for lower wave numbers; we show that the -1 scaling is from regions affected by shear.

Speaker:

Dr. Srimanta Middey

Affiliation:

Department of Physics, University of Arkansas, USA

Title:

Heterointerface Engineering of Correlated Oxides

Date:

14th April 2015 (Tuesday)

Time:

4 PM

Venue:

FB-382

Abstract:

Periodic geometrical arrangement of the constituent atoms in a crystalline solid is the backbone of electronic and magnetic properties. The alternation of this atomic arrangement, by creating interface between two chemically, electronically and structurally dissimilar materials can be expected to result a set of many-body states, which are unattainable in the constituent bulk materials. As the strong intercoupling among spin, charge, orbital, lattice degrees of freedom in correlated oxides promote various fascinating collective phenomena (e.g. superconductivity, magnetism, ferrolectricity ...), the additional broken symmetries and frustrated couplings across interface may give rise to a new horizon to novel electronic, magnetic and topological states. However, microscopic understanding of such interfacial properties is a grand challenge and it requires various advanced techniques. In this talk, I will illustrate the success in creating `new’ electronic states by growing transition metal oxide superlattices with unit cell precision. The implementation of synchrotron diffraction, x-ray absorption spectroscopy, resonant x-ray scattering experiments to elucidate the response of the underlying structures, spins, orbitals and charges due to this heterostructuring will be also discussed. Additionally, I will present the prospect of such engineered heterointerfaces for energy harvesting and application as next generation materials for Mott electronics.

Speaker:

Auditya Sharma

Affiliation:

Tel Aviv University, Israel

Title:

Landauer current and mutual information

Date:

14th April, 2015

Time:

2.30 PM

Venue:

FB-382

Abstract:

We study quantum evolution of the density matrix of a quantum dot con- nected to left and right leads initially maintained at chemical potentials µL and µR respectively and temperature T, within the non-interacting resonant-level model. The full nonequilirbium mixed state density matrix of the whole system is written down exactly, and the mutual information of the dot with respect to the leads is computed. A strong and direct correlation is found between the Landauer current, and the mutual information at all times, the steady-state values in particular displaying a quadratic relationship at high temperatures. We argue that this relationship could potentially be exploited experimentally to ‘measure’ mutual information. I will try to give an elementary introduction and build up the technical details gradually.References: [1] Auditya Sharma and Eran Rabani. Phys.Rev.B 91, 085121 (2015).

Speaker:

Gagan Kumar

Affiliation:

IIT Guwahati

Title:

Terahertz Plasmonic Waveguides

Date:

9-April-2015 (Thursday)

Time:

3 PM

Venue:

FB-382

Abstract:

Plasmonic metamaterials have the ability to facilitate the next generation miniaturized high speed communication devices and networks. In my talk, I will discuss about the design, fabrication and characterization of the terahertz guided wave devices on the planar surfaces using plasmonic metamaterials. Thin metal films when periodically corrugated with subwavelength scale structures forms a plasmonic waveguide, which can result in the propagation of terahertz modes confined in both the transverse directions. The degree of confinement and frequency of the resonant modes can be controlled with the geometrical parameters of the structures. In my talk, I will also discuss about the possibly of replacing metals substrates with semiconductors for such waveguide which can be advantageous in making active components.

Speaker:

Dr. R. Prabhu

Affiliation:

HRI, Allahabad

Title:

Multipartite quantum correlations in many-body systems.

Date:

8th April, 2015 (Wednesday)

Time:

4 PM

Venue:

FB-382

Abstract:

The cross-braiding between quantum information and condensed matter physics has recently stimulated excitation among researchers. Many-body systems are potential physical substrates to realize several quantum information protocols. The tools developed in quantum information have been put to use in analyzing collective phenomena in many-body systems. Many-body systems have been studied by observing, for example, their response to external perturbations, various order parameters, and excitation spectra. In this talk, I will characterize the behavior of several quantum correlation measures, including bipartite and multipartite ones, in spin models like Heisenberg spin system, XY-spin chain, etc. Also, I deal with the characterization of multipartite quantum correlation in spin models which can be both clean and disordered ones.

Speaker:

Dr. Arijit Kundu

Affiliation:

IU Bloomington, IN, US

Title:

Topology and Transport in Periodically Driven Systems

Date:

31st March, 2015 (Tuesday)

Time:

4 PM

Venue:

FB-382

Abstract:

One way to introduce topological phases in certain systems is periodic driving. For example, an 1D p-wave superconductor, driven periodically, can go through a Floquet transition to become topologically non-trivial. Such Floquet topological superconductor can host exotic steady states, which are called Floquet Majorana fermions. Whereas, graphene, under the application of circularly polarized laser is an example of Floquet topological insulator. Such topological insulators, like the quantum-hall systems, have non-trivial topology and chiral edge states. Such systems present potential applications to various fields from quantum computation to valleytronics. In this talk I'll present our recent works on topological classification and some novel transport characteristics of such driven systems.

Speaker:

Dr. Veeresh Singh

Affiliation:

University of KwaZulu-Natal Durban, South Africa

Title:

Unveiling the population of distant radio galaxies and their environments

Date:

31st March, 2015 (Tuesday)

Time:

12 noon

Venue:

FB-382

Abstract:

Radio galaxies exhibit jet-lobe radio structures emanating from active nucleus and are found to be hosted in massive elliptical galaxies. Radio galaxies particularly at higher redshifts and in obscured environments can be used as beacon to identify active galaxies and understand their evolution. It has been shown that Ultra Steep Spectrum (USS) radio sources are one of the efficient tracers of powerful High-z Radio Galaxies (HzRGs). We study properties of a USS sample derived from deep 325 MHz and 1.4 GHz observations and find a substantial population of unexplored weaker radio galaxies potentially hosted in obscured environments along with the population powerful HzRGs. Furthermore, in general, powerful HzRGs tend to reside in (proto)cluster environments.

Speaker:

Dr. Debakanta Samal

Affiliation:

Max-Planck Institute, Munich, Germany

Title:

Tailoring the electronic properties of cuprate layers on unit cell level: A boost towards designing artificial high Tc cuprates.

Date:

26th February, 2015 (Thursday)

Time:

4.30 PM

Venue:

FB-382

Speaker:

Dr. Dinesh Narayana Naik

Affiliation:

Department of Physics, Mehsana Urban Institute of Sciences, Ganpat University

Title:

Correlation holography: A marriage of holography with statistical optics

Date:

25th February, 2015 (Wednesday)

Time:

4 PM

Venue:

FB-382

Abstract:

With unconventional holographic techniques incoherent holography, coherence holography and photon correlation holography, it is possible to record and reconstruct 3-D objects as the second or fourth order correlation function of the optical fields. Unlike conventional holography, these techniques require only incoherent light for the illumination. The reconstructed object manifests itself in the spatial coherence function of the optical field. As a consequence, we can extend the holographic imaging to phenomena such as fluorescence with possible biomedical applications. Moreover, optical fields with a desired spatial coherence function can be synthesized using the technique of coherence holography with possible applications to microscopy and lithography.

Speaker:

Dr. Vishwanath Shukla

Affiliation:

IISc, Bangalore

Title:

Particles And Fields In Superfluids: Insights From The Two-Dimensional Gross-Pitaevskii Equation.

Date:

23th February 2015 (Monday)

Time:

4 PM

Venue:

FB-382

Abstract:

We study the dynamics of active particles in two-dimensional superfluids at temperature T = 0, for a variety of initial configurations, by carrying out extensive direct-numerical-simulations of the two-dimensional, Galerkin-truncated Gross-Pitaevskii equation. Our study elucidates the interplay of particles and fields, in both simple and turbulent flows. We show that particle collisions can be inelastic, if the repulsive interactions between particles is weak, and elastic otherwise. We show that assemblies of many particles and vortices yield turbulent spatiotemporal evolutions.

Speaker:

Hilal Ahmed

Affiliation:

AMU, Aligarh

Title:

Synthesis and Characterization of Nanocrystalline Colossal
Magnetoresistive Manganites

Date:

13th February 2015 (Friday)

Time:

11 am

Venue:

FB-382

Abstract:

In this talk, I shall present results obtained on nanocrystalline Sr-doped LaMnO₃. The parent material LaMnO₃ is an antiferromagnetic insulator at room temperature. Strontium (Sr) doped LaMnO3 is an interesting manganite which shows ferromagnetism at room temperature with a rich phase diagram. These materials are well suited for spintronics and biomedical applications

Speaker:

Dr. Debi Prasad Datta

Affiliation:

Institute of Physics (IoP), Bhubaneshwar

Title:

Ion beam induced synthesis and modifications of nano structures:
Fundamentals and some applications.

Date:

14th January, 2015 (Wednesday)

Time:

12 pm

Venue:

FB-382

Abstract:

Ion bombardment of solids is an efficient route towards processing of nano-scale surface patterns as well as synthesis and modification of nanostructures. Ion-beam-patterned surfaces are receiving increasing interest due to their promising applications, e.g., as templates for growing thin films with tailored properties. In this talk, I shall present our experimental investigations on the evolution of surfaces under off-normally incident medium energy ion bombardment. In fact, I shall show that ripple pattern evolution on Si[1], Ge[2], or SiO2 can be understood in a common theoretical framework, viz. as a result of ion erosion and ion induced mass redistribution. Irradiation-induced transition of such sinusoidal ripple patterns to a saw-toothed one will be demonstrated, which will be correlated to slope-dependent non-linear effect and shadowing of the incident ion beam. On the other hand, similar off-normal ion bombardment will be shown to result in no surface patterning but development of a porous structure containing nanofibers in case of GaSb and InSb [3], owing to growth of voids during bombardment. Some properties of such ion-induced structures, like photoluminescence, antireflection and hydrophobicity, will be discussed. In the last part of the talk, I shall describe studies on synthesis and modification of embedded Au nanoparticles in SiO2 by MeV Au2+-ion bombardment [4].
1. D. P. Datta et al., Phys. ReV. B 69, 235313 (2004); Phys. Rev. B 71, 235308 (2005); Phys. Rev. B 76, 075323 (2007), S. K. Garg and D. P. Datta
et al., Appl. Surf. Sci. 310, 147 (2014); Appl. Surf. Sci. 317, 476 (2014).
2. D. P. Datta et al., (to be communicated to Phys. Rev. B).
3. D. P. Datta et al., J. Appl. Phys. 115, 123515 (2014); Applied Surface Science 310, 189 (2014); J. Appl. Phys, 116, 033514 (2014); J. Appl. Phys. 116, 143502 (2014).
4. D. P Datta et al., Appl. Surf. Sci. 310, 164 (2014).

Speaker:

Faraz Ahmed Inam

Affiliation:

Dept. of Physics, Aligarh Muslim Universiuty

Title:

Fundamental characterisation of nanodiamond nitrogen-vacancy (NV) centres spontaneous emission as a single photon source.

Date:

06 January 2015 (Tuesday)

Time:

3 pm

Venue:

FB - 382

Abstract:

With its inbuilt, unique spin and optical properties, negatively charged nitrogen-vacancy (NV) centres in diamond have attracted wide interest in interdisciplinary research fields, ranging from quantum technologies, high-resolution magnetometry to biomedical imaging and tracking. Most of the highly sensitive applications of diamond-NV centers in the above fields rely on bright, controllable and photo-stable NV luminescence from very small diamond nanocrystals. Nanodiamond NV centre has been widely studied in the past decade and significant enhancements in its emission rate and capture factors were achieved. Nevertheless a complete picture of its spontaneous emission under the influence of the local electromagnetic nano-environment was non-existent at the beginning of my research study. In my research, I sought to improve the understanding of NV emission by systematically isolating the various individual mechanisms influencing its emission.

In this talk, I will shows how the systematic approach of our study of nano diamond NV emission under a range of conditions and environments elped us to develop and contribute towards the evolved understanding of
its spontaneous emission.

Speaker:

Dr. Swapnil Patil

Affiliation:

Tata Institute of Fundamental Research (TIFR)

Title:

Photoemission insight into exotic low temperature physics of
rare-earth intermetallics: heavy-fermion behaviour, mixed valency,
Kondo physics etc.

Date:

6th January, 2015 (Tuesday)

Time:

12 pm

Venue:

FB - 382

Abstract:

In this talk, I shall present the results of photoemission studies of remarkable Ce- and Yb- based materials, exhibiting unique properties like Kondo physics, heavy-fermion behaviour, and mixed valency. One of the important problems in correlated electron systems concerns the observation of "large-small" Fermi surface transition in Kondo systems with temperature. It is believed that the Fermi surface of a Kondo system expands at lower temperatures due to the formation of many-body Kondo singlet states. Our photoemission results however demonstrate temperature invariant Fermi surface in a prototypical Kondo system, YbRh2Si2. Additionally our results on Ce-Kondo systems demonstrate electronic spectral evolution which deviates from the predictions of Anderson model, a theoretical model normally used to interpret photoemission spectra from Kondo systems. Potential candidates to explain these discrepancies will be briefly discussed. Finally Fermi surface studies on YbCo2Si2, a stable valent Kondo lattice, will be discussed which serves as a reference compound for YbRh2Si2, which happens to be close to quantum criticality.