Talks

Illuminating a material with light can reveal both interesting aspects of electronic and lattice degrees of freedom, as well as drive phase and topological transitions in the material itself. In this talk, I will focus on three distinct responses of a material to light: (1) Nonlinear phononic control of magnetism in bilayer CrI3, MnBi2Te4, and MnSb2Te4. (2) The non-linear photogalvanic response of Weyl semimetals with tilted cones and chiral charge up to 4 (the largest allowed in a lattice model), as well as the topological superconductor candidate 4Hb-TaS2, and (3) The coupling of phonons to electronic degrees of freedom to produce chiral phonons with large g-factors of order 1, which can be measured with Raman scattering. For nonlinear phononic control of magnetism, I will show how intense THz light can be used to transiently modify magnetic exchange constants, including their sign. In the case of the non-linear current response of Weyl systems, I will review how the quantum geometry...

Computer Engineered 2D Materials: Host for Unconventional Properties

Tanusri Saha-Dasgupta
S. N. Bose National Centre for Basic Sciences, Kolkata 700106, INDIA

In this talk, we will discuss two computer-engineered 2D materials, which are predicted to host unconventional topological properties. The first problem to discuss is robust half-metallicity and topological properties in square-net potassium manganese chalcogenides, paving the way to design topological half-metals and application possibilities in topological quantum spintronics.[1] The second problem deals with the giant Rashba effect and nonlinear anomalous Hall conductivity in a two-dimensional molybdenum-based Janus structure. With strong spin-orbit coupling and inversion symmetry broken by asymmetric surface passivation in these 2D MXene compounds, a giant Rasbha effect and a simultaneous appearance of nonlinear anomalous Hall conductivity.[2]

[1] Koushik Pradhan, Prabuddha Sanyal, and Tanusri Saha-Dasgupta, Phys. ...

Spontaneous synchronization is at the core of many natural phenomena. Your heartbeat is maintained because cells contract in a synchronous wave; some bird species synchronize their motion into flocks; quantum synchronization is responsible for laser action and superconductivity. The transition to synchrony, or between states of different patterns of synchrony, is a dynamical phase transition that has much in common with conventional phase transitions of state – for example solid to liquid, or magnetism – but the striking feature of driven dynamical systems is that the components are “active”. Consequently quantum systems with dissipation and decay are described by non-Hermitian Hamiltonians, and active matter can abandon Newton’s third law and have non-reciprocal interactions. This substantially changes the character of many-degree-of-freedom dynamical phase transitions between steady states and the critical phenomena in their vicinity, since the critical point is an “exceptional point...

Inspired by the observation of crystallization of the vortices in the intermediate field range in a Kitaev model [Phys. Rev B 108, 165118 (2023)], we delve into obtaining different superlattice formations of the vortices and the corresponding Majorana dispersions. This gives a novel possibility of governing flat bands for Majoranas and other possible excitations that may arise in analogous settings. We find several superlattice configurations of vortices where Majorana states are weakly dispersive or even fully flat with or without a gap. The gapped flat bands have a non-zero Chern number with a higher quantum metric value (bandwidth) tunable by varying applied magnetic fields. Having satisfied the ‘vortexibility condition,’ these bands can harbor fractional Chern insulator phase of the emergent Majorana fermions if appropriate interactions are present. Interestingly, we have used the projection method and maximally localized Wannier functions algorithm to identify the localizing c...