Talks on 1st April 2024 

Prof. Sunandan Gangopadhyay (10:00 am - 10:20 am)

Title: Research directions in our department

Abstract: The research activities in our department which are primarily theoretical will be presented. The thrust areas which we focus on are gauge/gravity duality, aspects of linear quantum gravity, black hole physics, conformal field theory and quantum field theory in curved spacetime. We hope that some of these areas will be of interest to the faculty members working in theoretical physics in Ashoka University.

Prof. Tapas Baug (10:20 am - 10:40 am)

Title: Accretion through filaments in massive protoclusters

Abstract: Filaments are found to be the predominant structures in Galactic star-forming clouds. These filaments are believed to play an important role in transporting molecular gas along their axes and create the necessary condition for star formation to occur. Dense star-forming cores may also form within these filamentary structures. In this presentation, I shall elaborate on whether and how filaments help in accreting gas onto the star forming core using protostellar outflows as a proxy.

Prof. Somak Raychaudhury (10:40 am - 11:00 am)

Title: Evolution of galaxies on filaments of the cosmic web

Abstract: TBD

Prof. Tanusri Saha-Dasgupta (11:30 am - 11:50 am)

Title: Understanding and Predictions: Materials Physics by Computation

Abstract: In this talk, we will discuss our recent effort on understanding and prediction of materials properties as well as new materials using the power of first-principles calculation, many-body methods and machine learning.

Dr. Atidra Pal (11:50 am - 12:10 pm)

Title: Transport phenomena in quantum materials to atomic/molecular scale devices

Abstract: In this talk, I will give an overview of research happening in our group: “Quantum transport and Devices

Lab”. Our research mainly focuses on studies of the mechanisms of charge and spin transport at the nanoscale devices to single molecular junctions. This understanding may lead to various applications ranging from ultralow noise electronics, sensors to device miniaturization. The following three research topics will be discussed briefly:

Transport through atomic and single molecular junction:

A single organic molecule suspended between two metallic electrodes is an attractive electronic device since it allows the rich structural possibilities of organic molecules to manipulate electronic conductance at the nanoscale. We will discuss how one can create a single molecular junction and study electron transport to get statistical information. I will discuss the role of metal/molecule interface, orientation of the molecule and the mechanical gating effect in a single molecular device.

2D materials and their hybrid devices

The isolation of graphene by a simple scotch-tape based technique has created a huge playground for exploring various two-dimensional (2d) layered materials due to their excellent electronic, optical, mechanical and thermal properties. I will discuss our recent focus on understanding the contacts in both ptype and n-type 2D semiconductors, the light matter interaction and optoelectronic devices in 2D hybrid. 

Charge density with topology and unusual magnetism in van der Waal Ferromagnet

We will focus on our recent work on metallic charge density wave system and will discuss how these transitions lead to nontrivial topology. Furthermore, I will show our recent results on Van der Waal Ferromagnet (Fe4GeTe2) exhibiting a spin reorientation transition. Through a combination of transport and ESR measurements we unravel emergent electronic phases in this system. 

Dr. Susmita Saha (12:10 pm - 12:30 pm)

Title: Spinwave Dynamics in Magnetic Nanostructures

Abstract: Magnonics is an exciting research field that promises a new generation of energy-efficient devices with a significant impact on information technology. The fundamental concept of magnonics is to use the counterpart of magnon, known as spinwaves, to carry and process information in the microwave regime. It holds the promise of a new generation of energy efficient devices with significant impact on information technology and emerged as a potential and alternative candidate of modern existing electronic technology. One of the key aspects of our research is the control of the spinwaves in a magnetic nanostructure with the potential to not only answer fundamental questions concerning magnonics but also to provide a new generation spinwave based devices. In this talk I will discuss about the manipulation of spinwave dynamics in various magnetic nanostaructures include magnetic fractals, magnetic skyrmions, ferrimagnetic thin films.

Dr. Garima Mishra (12:30 pm - 12:50 pm)

Title: Compaction and melting of DNA

Abstract: I will discuss about the compaction of DNA by considering two types of effective interactions, (i) inter-strand native-pair interactions that favour dsDNA formation, and (ii) intra-strand native-pair interactions that promote the folding of each strand of DNA. The varying strengths of these effective interactions mimic the role of different cellular environments that lead to the compaction of DNA inside the cell. I will show that DNA takes an overall sheet-like structure in the region where an incipient transition to a compact phase would have occurred. The stability of this phase is due to the extra entropy from the folding of the sheet, which is absent in the remaining polymer-like states of the phase diagram. The compact DNA melts along the specified line in the phase diagram, where the ratio of effective interactions is unity.

Prof. Dipankar Bhattacharya (3:00 pm - 3:20 pm)

Title: Polarized High Energy emission from cosmic sources

Abstract: Polarization of radiation from an astronomical source serves as an important diagnostic of non-thermal emission, magnetic fields, scattering processes and geometrical anisotropies. Polarisation at X-ray and Gamma-ray bands have been difficult to measure, but this area is now opening up with new and recent space missions. This talk will discuss some recent results obtained with the Indian mission AstroSat.

Prof. Kandaswamy Subramanian (3:20 pm - 3:40 pm)

Title: To B or not to B or both

Abstract: We combine semi-analytic models of galaxy formation and dynamo models of magnetic field generation to predict the radio luminosity function (RLF) of star forming galaxies and its cosmological evolution. We find reasonable agreement with existing data at redshifts below unity, but increasing tension with observations at higher redshifts, indicating the inadequacy of current models when applied to high redshift galaxies. Both the small- and large-scale magnetic fields contribute to the RLF but the small-scale field dominates at high redshifts. Polarisation observations, by upcoming radio telescopes, will therefore be important to distinguish these two components and understand better the evolution of galaxies and their nonthermal constituents.

Reference: arXiv preprint arXiv:2402.15099 by Jose et al, 2024

Dr. Suratna Das (3:40 pm - 4:00 pm)

Title: Warming up Cosmic Inflation

Abstract: Cosmic Inflation, despite being still a paradigm, has become an integrated part of Modern Cosmology. Hence, it is important to assess the various competing theories of inflationary dynamics to better understand the evolutionary history of our universe. The theories of cosmic inflation can be broadly categorized into two classes: Cold inflation and Warm Inflation. Cold inflation, being a comparatively simpler dynamics of inflation which is also in good agreement with the observations, has been explored extensively in the literature. On the other hand, Warm Inflation, though theoretically well motivated than Cold Inflation, has been explored far less than Cold Inflation due to its complex dynamics. In this talk, I will try to motivate Warm Inflation and will lay out possible collaborations that I can have with SNBNCBS faculties in this active field of research. 

Prof. Gautam Menon (4:40 pm - 5:00 pm)

Title: Understanding slow axonal transport

Abstract: Small molecular-size machines called molecular motors help to transport cargo along the long processes of nerve cells. There are two types of such transport, called slow and fast. While the fast axonal transport of cargo in axons is by now well understood, the nature of slow transport remains controversial and, in particular, how mechanisms for slow axonal transport are modulated during development is unexplored. We study a number of different models for slow axonal transport, comparing their predictions to data on transport of the enzyme choline acetyltransferase (ChAT) in sensory neurons of Drosophila larva, across developmental stages. We show that accounting for changes in the diffusive fraction of cargo during these developmental stages is essential and that diffusion cannot be neglected in the modeling of the slow axonal transport of small soluble proteins. Where our work differs from earlier model approaches is in our attempt to see what models and parameters could best describe data from experiments on a specific protein known to be transported via slow transport and in the detailed benchmarking of theory to experiment. 

Prof. Rajiv Mitra (5:00 pm - 5:20 pm)

Title: Biomolecular Condensation

Abstract: Biomolecules, specifically proteins, under specific environments (e.g., temperature, pressure, pH, ionic strength etc.) undergo phase transition from monomeric to aggregates. This phenomenon, commonly known as biomolecular condensation, has attracted attention of biophysicists due to its inherent complexity and potential therapeutic applications. While most of the earlier studies in this direction has been performed from protein’s perspective, little attention has been paid on the pivotal role of solvation during the phase transition. Using THz (1 THz=10 12 Hz) spectroscopy, we are trying to unravel the role of hydration on biomolecular condensation.

Dr. Saquib Shamim (5:20 pm - 5:40 pm)

Title: Cold systems and small devices

Abstract: In this talk, I will give an overview of the research work carried out in our lab. Our group's expertise is measuring electrical transport in mesoscopic devices made from various semiconducting materials at ultra-low temperatures. We use these measurements to investigate various concepts in solid-state physics. Over the past few years, our interest has been in investigating interfaces of materials with mutually inverted band-structure. Such systems host gapless surface/edge channels protected against single-particle elastic backscattering under time-reversal symmetry, resulting in dissipationless transport. Currently, we are investigating such surface/edge states in transition metal dichalcogenides.

Dr. Arijit Halder (5:40 pm - 6:00 pm)

Title: Recent trends in condensed matter physics: Non-Fermi liquids, Topology and Entanglement

Abstract: Recently, condensed matter physics has seen the emergence of several new concepts in areas such as non-Fermi liquid theory, topological phases, and quantum entanglement. In this talk, I will briefly introduce our group's research activities to push these ideas forward. In particular, I will talk about developments in non-Fermi liquid research, which aims to answer questions in phases of matter lacking quasiparticles. Next, I will briefly introduce higher-order topology, a new concept in topological condensed matter systems, and discuss our work in this area. In the last part of the talk, I will focus on quantum entanglement in many-body systems and briefly describe a new field-theoretic interpretation for computing entanglement in these systems.

Talks on 2nd April 2024 by PhD Scholars

Riya Mehta (9:30 am - 9:40 am)

Title: Static and Dynamics Magnetic Characterization of CoFeB/NiO/CoFeB Trilayers

Abstract: With the advent of giant magnetoresistance, there has been significant attention directed towards investigating interlayer exchange-coupled configurations. These configurations involve connecting two ferromagnetic layers through a spacer layer. Trilayers with the configuration FM/AFM/FM possess two interfaces that are jointly shared between the ferromagnetic and antiferromagnetic layers. This unique system results in exchange coupling at these interfaces, making the investigation of spin transport and relaxation within such systems fascinating and opening up possibilities for their utilization in magnonics applications. Here, we aim to explore interlayer exchange coupling, magnetic damping, and magnetisation reversal in CoFeB/NiO/CoFeB trilayers by varying the NiO thickness for their potential application in magnonic devices.

Souradeep Sengupta (9:40 am - 9:50 am)

Title: Thermal melting of circular DNA

Abstract: We investigate the melting transition of non-supercoiled circular DNA of different lengths, employing Brownian dynamics simulations. In the absence of supercoiling, we find that melting of circular DNA is driven by a large bubble, in agreement with earlier studies of circular DNA melting in the presence of supercoiling. By analyzing sector-wise changes in average base-pair distance, our study reveals that the melting behavior of non-supercoiled circular DNA closely resembles that of linear DNA. Additionally, we find a marked difference in the thermal stability of circular DNA over linear DNA at very short length scales, an effect that diminishes as the length of the molecule increases. The stability of smaller circular DNA is linked to the occurrence of transient small bubbles, which are characterized by a lower probability of growth.

Shri Gowri Tikoti (9:50 am - 10:00 am)

Title: Collective dynamics of C. elegans in 3D and 2D

Abstract: Critical phenomena in biological systems are proving to be more common. To understand it, we need to know the emergent behaviors of the active agents. Less is known about the collective behavior when the active agents are bidirectional and flexible. This talk highlights the work undertaken so far in the collective dynamics of C. elegans in 3D and 2D.

Philip Cherian (10:10 am - 10:10 am)

Title: Hybrid immunity and school reopenings: an agent-based study

Abstract: The spread of infectious diseases is often modelled through either equation-based or agent-based approaches. While equation-based models tend to be less computationally intensive and are faster to run, they are deterministic by construction, and often exclude information contained in real-world networks of physical interactions. On the other hand, agent-based models allow for a more comprehensive understanding of disease spread and its social determinants by accounting for individual-level heterogeneity, with individual agents in these models capable of modulating their behaviour in response to their environment, contact networks, and geo-spatial data.

In this talk I will describe a versatile new agent-based simulation framework, BharatSim. I will use BharatSim to address a specific question in the context of epidemiology: When can schools be safely reopened in the background of a pandemic? I will also discuss how this result depends on specified levels of hybrid immunity, that is, immunity derived from a combination of vaccination and prior infection.

Anantharaman S V (10:10 am - 10:20 am)

Title: Are pulsar glitches Bactrian?

Abstract: Pulsars are rotating neutron stars whose radiation sweeps past the earth every few seconds. But, occasionally, the rate of rotation increases and subsequently relaxes. Such an event is referred to as a glitch. This is thought to result from the large-scale unpinning of superfluid vortices in the star's crust. Such glitches could be of various sizes and could last for various durations. The size distribution of these features is widely quoted as lognormal or exponential. We revisit the observational data and question the validity of the mentioned fits. We find a possible bimodality in the distribution, very reminiscent of the Bactrian camel.

In this talk, we delineate our efforts to understand, using a computationally simple n-body simulator, the nature of processes that could create a bimodal glitch-size distribution.

Aditya Jain (10:20 am - 10:30 am)

Title: Correlation functions in superconformal theories

Abstract: Conformal symmetry completely fixes the 2 and 3-pt correlation functions of all the operators in a QFT. In a supersymmetric conformal field theory (SCFT), we implement similar techniques to determine the correlation functions of conserved operators. We find structures which are superconformally invariant, use their linear combination to construct the correlator, and apply the conservation condition to completely fix the form. We use auxiliary spinors to encode the spin of the operator, thus enabling the computation for any arbitrary spin correlator.

Umang Kumar (10:30 am - 10:40 am)

Title: Cosmic Inflation: Can It Be Warm?

Abstract: Cosmological Inflation refers to a brief period of accelerated expansion in the early history of the Universe. Proposed to tackle the limitations/problems of the Big Bang Cosmology, the theory has been successful at explaining the origins of the structure of the Universe through the perturbations of a (hypothetical) scalar field dubbed Inflaton. The observations of the Cosmic Microwave Background (CMB), most recently by Planck, provides a way to test the Inflationary paradigm. An alternative to the standard Inflationary paradigm, known as Warm Inflation has been recently (Berera, 1995) proposed which involves the decay of Inflaton into a radiation bath during inflation. In this talk, we will try to motivate and explore more about Warm Inflation with an emphasis on the differences between the two paradigms.