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Monday, 23 December 2019
Time Speaker Title Resources
09:45 to 10:20 Arnab Sen (Indian Association for the Cultivation of Science, India) Disorder in a classical spin liquid: topological spin glass, cluster algorithm and dynamical Griffiths phase
10:20 to 10:55 Yasir Iqbal (IIT - Madras, India) Quantum spin liquids in pyrochlore magnets: a functional renormalization group perspective
10:55 to 11:25 Break Tea/coffee
11:25 to 12:00 Suraj Hegde (Max Planck Institute for physics of complex systems, Dresden) Hawking-Unruh Thermality and Quasinormal quantised time decay in dynamics on lowest Landau levels
12:00 to 12:35 Soumya Bera (IIT - Bombay, India) Dynamics in many-body localized system
12:45 to 14:00 Lunch Lunch
14:00 to 14:35 Debanjan Chowdhury (Cornell University, USA) Strong coupling superconductivity and pseudogap in topological flat bands
14:35 to 15:10 Subroto Mukerjee (IISc., India) Bilayer graphene and twisted bilayer graphene: Specular Andreev reflection and thermoelectricity
15:10 to 16:00 Break Tea/coffee
16:00 to 17:00 Ashvin Vishwanath (Harvard University, USA) INFOSYS-ICTS Chandrasekhar Lectures : Entanglement and Topology in Quantum Solids (Lecture 1)
Tuesday, 24 December 2019
Time Speaker Title Resources
09:30 to 10:05 Haruki Watanabe (University of Tokyo, Japan) Symmetry indicators of topological superconductors
10:05 to 10:40 Abhishodh Prakash (ICTS-TIFR, Bengaluru, India) Emergent symmetries in invertible phases.
10:40 to 11:10 Break Tea/coffee
11:10 to 11:45 David Carpentier (ENS de Lyon, France) Topological pumping: from the Quantized Hall Effect to circuit QED
11:45 to 12:20 Krishnendu Sengupta (Indian Association for the Cultivation of Science, India) Floquet engineering of quantum scars
12:30 to 14:00 Break Lunch
14:00 to 14:35 Vikram Tripathi (TIFR, Mumbai, India) Deconfinement in Heisenberg-perturbed Kitaev models: A Fock space localization perspective

The two widely studied Kitaev materials, α-RuCl3 and Na2IrO3 , have magnetically ordered ground states although the dominant interparticle interactions are Kitaev like. Manipulating these Kitaev materials to access Kitaev physics is an open experimental and theoretical challenge. A point of intense current debate is whether there is any parameter regime where the many-body excitations in the ordered phase clearly resemble those of the Kitaev model (i.e. deconfined Majorana fermions and visons) and not something more mundane, such as magnons. Furthermore, there is no consensus on the parameter regime where Kitaev physics, if any, may be seen. It is not clear whether one should (a) suppress the magnetic order using, say, an external field (suggested by quantized thermal Hall effect) and look at low-energy excitations, or (b) explore excitations with energies higher than the magnetic ordering scale since the Kitaev interactions are by far the most dominant (suggested by neutron scattering data). To attack these open questions, we propose a new approach of directly comparing the many-body states of a Kitaev-Heisenberg model with pure Kitaev states as well as magnon-like excitations of a spin-density wave. We cast the problem as one of many-body localization. This approach requires evaluation of a large number of excited states, for which we have used the state-of-the-art FEAST exact diagonalization technique. Our main finding is that over a range of strengths of the Heisenberg perturbation where spin-density wave order is present, the low-lying excitations resemble Kitaev states rather than magnons. Higher energy excitations, above the magnetic ordering scale, surprisingly do not resemble Kitaev or magnon excitations. Our ability to calculate high excites states also allows us to report for the first time the evolution of the vison gap as a function of the Heisenberg perturbation, A key observation that we make is that the vison gap – a characteristic of the deconfined Kitaev spin-liquid phase - persists well into the proximate magnetically ordered phase.

14:35 to 15:10 G Baskaran (IMSc, India) Navigating the Hilbert Space with Models

In recent times, some fascinating models have helped us find fascinating corners in Hilbert spaces of quantum matter. Hilbert space is an incomprehensibly big, wild and turbulent ocean. Models help us in our voyage. After brief review of spin liquid models of Anderson, Sachdev, Ye and Kitaev, I will discuss our recent results [1] on `Kitaev clusters'. Even in a finite dimensional Hilbert space, some manifolds unique to the model emerge and guide us.

15:10 to 16:00 Break Tea/coffee
16:00 to 17:00 Ashvin Vishwanath (Harvard University, USA) INFOSYS-ICTS Chandrasekhar Lectures : Topology, correlations and superconductivity in magic angle.. (Lecture 2)
Thursday, 26 December 2019
Time Speaker Title Resources
09:30 to 10:05 H. R. Krishnamurthy (IISc., India) Correlation induced metallic, half-metallic and superconducting phases in strongly correlated band Insulators.
10:05 to 10:40 Srimanta Middey (IISc., India) Shining X-ray on Oxide Heterostructures

Oxide heterostructures are host of many emergent phenomena, which are very often “hidden” or unattainable in the constituent bulk materials. While the strong interplay among spin, charge, orbital, lattice degrees of freedom facilitate interesting many-body quantum phenomena in correlated oxides, the additional broken symmetries and frustrated couplings across the interface of artificial heterostructures may give rise to new electronic, magnetic states. However, microscopic understanding of these phenomena in ultrathin films is very challenging. In this talk, I will discuss about emergent electronic and magnetic phases in several artificial structures of rare-earth nickelates and high Tc cuprates. The results of synchrotron diffraction, x-ray absorption spectroscopy, resonant x-ray scattering will be presented.

10:40 to 11:10 Break Tea/coffee
11:10 to 11:45 Amit Agarwal (IIT - Kanpur, India) Quantum Anomalies and magneto-transport in Weyl semimetals

Quantum anomalies in Weyl semimetal (for either E · B ̸= 0 or ∇T · B ̸= 0) leads to chiral charge and energy pumping between the opposite chirality nodes. This results in chiral charge and energy imbalance between the Weyl nodes which manifests in several intriguing magneto-transport phenomena. Here, we investigate the role of electrical-, thermal-, and gravitational chiral anomaly on magneto-transport in Weyl semimetals. We predict the planar Ettinghausen and Righi-Leduc effect to be a distinct signature of these quantum anomalies. We also demonstrate a significant enhancement in the thermo-electric conductivity, Seebeck effect, Nernst effect and thermal con- ductivity with increasing temperature. Interestingly, this anomaly induced transport violates the Wiedemann-Franz law and Mott relation.

11:45 to 12:20 Tanusri Saha-Dasgupta (S N Bose National Center for Basic Sciences, India) Tailoring Topological Phases: A Materials Perspective
12:30 to 14:00 Break Lunch
14:00 to 14:35 Assa Auerbach (Technion Israel Institute of Technology, Israel) What determines the Hall and Thermal Hall signs of metals, magnets and superconductors?
15:00 to 16:00 Ashvin Vishwanath (Harvard University, USA) INFOSYS-ICTS Chandrasekhar Lectures : Surface topological order - uniting `integer' and `fractional' topological states (Lecture 3)
16:00 to 17:00 Break Tea/coffee
17:00 to 18:00 Srikumar Banerjee ICTS Foundation Day Lecture: The Beta (bcc) to Omega (hexagonal) Phase Transition: A Unique Example
Friday, 27 December 2019
Time Speaker Title Resources
09:30 to 10:05 Tarun Grover (University of California San Diego, USA) Detecting finite-temperature topological order.
10:05 to 10:40 Sankalpa Ghosh (IIT - Delhi, India) Magnetic Hofstadter butterfly and topological quantization of Hall conductivity in Graphene
10:40 to 11:10 Break Tea/coffee
11:10 to 11:45 Dam Thanh Son (University of Chicago, USA) Kelvin circulation theorem, dynamic metric and the fractional quantum Hall effect

We construct a hydrodynamic theory describing the low-energy dynamics of quantum Hall Jain states near half filling. The theory has the form of a hydrodynamic theory with a dynamic metric tensor. We show the existence of a generalization of the Kelvin circulation theorem and deduce information about the structure factor from this theorem.

11:45 to 12:20 Ajit Balram (IMSc, India) Parton paradigm for the quantum Hall effect

The fractional quantum Hall effect (FQHE) forms a paradigm in our understanding of strongly correlated systems. FQHE in the lowest Landau level (LLL) is understood in a unified manner in terms of composite fermions, which are bound states of electrons and vortices. The strongest states in the LLL are understood as integer quantum Hall states of composite fermions and the compressible 1/2 state as a Fermi liquid of composite fermions. For the FQHE in the second LL, such a unified description does not exist: experimentally observed states are described by different physical mechanisms. In this talk, I will discuss our first steps towards a unified understanding of states in the second LL using the ``parton" theory. I will elucidate in detail our recent work on the parton construction of wave functions to describe many of the FQH states observed in the second LL.

12:30 to 14:00 Break Lunch
14:00 to 14:35 Erez Berg (Weizmann Institute of Science, Israel) New physics in Moire superlattices
14:35 to 15:10 Sumiran Pujari (IIT - Bombay, India) Beyond-Dirac fermions in a three-band Graphene-like model
15:10 to 15:40 Break Tea/coffee
Monday, 30 December 2019
Time Speaker Title Resources
09:30 to 10:05 Ganpathy Murthy (University of Kentucky, USA) Surface states and arcless angles in twisted Weyl semi-metals
10:05 to 10:40 Mandar Deshmukh (TIFR, Mumbai, India) Tunable gaps and bandwidths in twisted double bilayer graphene system on the verge of correlations.
11:10 to 11:45 Hridis Kumar Pal (IIT - Bombay, India) Emergent geometric frustration and flat bands in twisted bilayer graphene
11:45 to 12:20 Rajdeep Sensarma (TIFR, Mumbai, India) Screening in twisted bilayer graphene
12:30 to 14:00 Break Lunch
14:00 to 14:35 Abhay Narayan Pasupathy (Columbia University, USA) Correlated states in van der Waals heterostructures
14:35 to 15:10 Arindam Ghosh (IISc., India) Thermoelectricity in twisted bilayer graphene
15:10 to 15:40 Break Tea/coffee
15:40 to 16:15 Brijesh Kumar (Jawaharlal Nehru Technological University, India) Inversion and quantum oscillations in Kondo insulators"
Tuesday, 31 December 2019
Time Speaker Title Resources
09:30 to 10:05 Yuval Gefen (Weizmann Institute of Science, Israel) interplay of symmetry and topology on the edge of quantum Hall systems
10:05 to 10:40 Anindya Das (IISc., India) Thermal Hall for fractional quantum Hall States of bilayer graphene

Electron-electron interactions in partially filled Landau levels gives rise to strongly correlated topological phase, known as the fractional Quantum Hall (QH) states whose edge structures are not as simple as in integer QH state. Moreover, the edge structures become more intricate or hole-conjugate states like ν = 2/3, 3/5 or 4/7. The frequently studied filling factor, ν = 2/3, was initially proposed to harbour two counter-propagating modes: a downstream ν = 1 and an upstream ν = 1/3, and expected to exhibit electrical conductance, G e = 4/3 e 2 /h. However, the charge equilibration between these modes always led to an observed downstream ν = 2/3 charge mode (G e = 2/3e 2 /h) accompanied by an upstream neutral mode. The energy equilibration between the downstream charge mode and upstream neutral mode is expected to exhibit total zero thermal conductance (G th ), which has been observed in GaAs/AlGaAs based systems. Here, we have carried out the electrical and thermal conductance of the hole-like fractional QH states (ν = 5/3 and 8/3) along with the particle-like fractional QH states (ν = 4/3 and 7/3) in graphite gated hBN encapsulated bilayer graphene. The measured electrical conductance with precise value of G e = 5/3 e 2 /h and 8/3 e 2 /h for ν = 5/3 and 8/3 strongly suggest the charge equilibration between the counter-propagating edges. The thermal conductance of the particle-like states of ν = 4/3 and 7/3 was found to be consistent with theoretically predicted values of G th = 2k 0 and 3k 0 (where, ). However, the observed value of thermal conductance of hole-like states ν = 5/3 and 8/3 with G th = 3k 0 and 4k 0 is strikingly different from earlier observation with values k 0 and 2k 0 in GaAs/AlGaAs with full equilibration of energy. Our results, hitherto not known, reveal the complex nature of equilibration of counter-propagating edges for hole-like fractional QH states in graphene.

10:40 to 11:10 Break Tea/coffee
11:10 to 11:45 Vijay B Shenoy (IISc., India) Fractonic Gauge Theories
11:45 to 12:20 R. Shankar (Yale University, USA) Equality of bulk wave functions and edge correlations in some topological superconductors: A spacetime derivation
12:30 to 14:00 Break Lunch
14:00 to 14:35 Ramachandran Shankar (IMSc, India) An approach to the quantum geometry of correlated states
14:35 to 15:10 S. R. Hassan (IMSc, India) Intrinsic and extrinsic geometries of correlated many-body states
15:10 to 15:40 Break Tea/coffee
15:40 to 16:15 T. V. Ramakrishnan (IISc., India) Theory of Linear Resistivity in Strongly Correlated Metals
17:00 to 19:00 Purna P Bangere Talk and concert
Wednesday, 01 January 2020
Time Speaker Title Resources
09:30 to 10:05 Zi Yang Meng (Institute of Physics Chinese Academy of Sciences, China) What we talk about When we talk about novel phases of quantum matter

In this talk, I will review recent developments in a priori and a posteriori numerical strategies in dealing with quantum many-body systems. Thanks to these philosophical and numerical advancements, new paradigms in condensed matter and high energy physics such as non-Fermi-liquid, quantum criticality and emergent gauge-field coupled with matter field can be accessed with large-scale numerical simulations. These results in turn inspire further analytical and numerical progress towards the complete form of few important many-body physics problems.

10:05 to 10:40 Kedar Damle (TIFR, Mumbai, India) Random Singlet susceptibility of a disordered exactly solvable SU(2) symmetric Majorana spin liquid with honeycomb lattice symmetries.
10:40 to 11:10 Break Tea/coffee
11:10 to 11:45 Fa Wang (Peking University, China) Impurity effects on the superconductivity in twisted bilayer graphene
11:45 to 12:20 Subir Sachdev (Harvard University, USA) Deconfined critical point in a doped random quantum Heisenberg magnet

We describe the phase diagram of electrons on an infinite cluster of sites, with random hopping and Heisenberg spin exchange interactions between any pair of sites. Double electron occupancy is prohibited on all sites. A perturbative renormalization group analysis yields a critical point with fractionalized excitations at a non-zero hole doping p away from the half-filled insulator; we carry out the renormalization group to two loops, but some exponents are obtained to all loop order. We argue that the critical point is flanked by confining phases: a disordered Fermi liquid with carrier density 1+p at higher doping, and a metallic spin glass with carrier density p at lower doping. Additional evidence is obtained from a large M analysis of a model which extends the SU(2) spin symmetry to SU(M). We note implications for the phase diagram of the cuprates.

14:00 to 14:35 Ady Stern (Weizmann Institute of Science, Israel) Josephson controlled topological superconductivity
14:35 to 15:10 Michael Fuhrer (Monash University, Australia) Atomically thin Na3Bi for topological electronics
15:10 to 15:40 Break Tea/coffee
15:40 to 16:15 Ribhu Kaul (University of Kentucky, USA) Quantum phase diagrams of two dimensional "designer" spin models

Quantum spin models are the simplest examples of many body systems. While tremendous progress has been made in understanding their phase diagrams in one dimension (chains and ladders) through the development of powerful analytic and numerical techniques, very little is known about their phase diagrams in two dimensions. Here I will present our work on this topic using models that are designed to be free of the sign problem of quantum Monte Carlo. In particular, I will focus on the role of the size of the spin on the phase diagrams of two dimensional bipartite spin systems and the demonstration of a topological spin liquid in a non-bipartite quantum spin model.

Thursday, 02 January 2020
Time Speaker Title Resources
09:30 to 10:05 Masaki Oshikawa (Institute for solid state physics, Japan) Flat bands in honeycomb networks
10:05 to 10:40 Tanmoy Das (IISc., India) Symmetry-broken topological phases

Time reversal (T), charge conjugation (C) symmetries, and their combination CT (chiral symmetry) constitute 10 distinct classes of topological phases, popularly known as ten-fold way. A closer look at the already known list of topological phases reveals that there exist even more topological phases which cannot be easily categorized within this ten-fold classification scheme. We extent the topological band theory to a wider symmetry classes, were a broken symmetry is recovered by other symmetries to commence a new topological phase and/or adiabatically connect to its parent phase. In fact, we will show some examples where none of the individual symmetries or their dual combinations are present, but a CPT (P = parity) combination emerges as the defining symmetry. Examples will also include real materials where a combination of DFT, tight-binding model, and Ginzburg Landau Chern-Simon theory is employed to study the interplay between topological excitation and magnetic collective modes.

10:40 to 11:10 Break Tea/coffee
11:10 to 11:45 Diptiman Sen (IISc., India) Some unusual topological systems --- spin waves and Josephson junctions

When an integrable system is driven periodically in time, it is known that the eventual steady state can be described by a generalized Gibbs ensemble. We will discuss what happens when an integrable system is driven aperiodically. In our study we will consider the one-dimensional Ising model in a transverse field which is driven in different ways. We will look at three kinds of aperiodic driving: driving with a random noise, with a scale-invariant sequence (Thue-Morse) and with a quasiperiodic sequence (Fibonacci). We find that a random noise leads to the infinite temperature ensemble while the Thue-Morse sequence eventually (after an astronomically long time) leads to a periodic steady state because of some conserved quantities. The Fibonacci sequence leads to a wide variety of long-time behaviors, which are generally neither periodic nor infinite temperature states. However some limiting cases lead to almost periodic steady states.

11:45 to 12:20 Sumathi Rao (HRI, Allahabad, India) Curvature function renormalisation and topological phase transitions
12:30 to 14:00 Break Lunch
14:00 to 14:35 Manish Jain (IISc., India) Flat bands in twisted bilayer transition metal dichalcogenides