Talks

2D van der Waals materials-based heterostructures have led to new devices for fundamental science and applications. Superconducting Josephson devices based on 2D materials offer unique opportunities to engineer new functionality for quantum technology. I will present results from two classes of materials. First, proximitized graphene-based Josephson junctions lead to a quantum noise-limited parametric amplifier with performance comparable to best discrete amplifiers in this class [1]. Gate tunability of the center frequency of the amplifier, rather than flux, offers key advantages. An extension of graphene Josephson architecture to make state-of-the-art bolometers leveraging graphene's low specific heat, and I will present initial results. Second, twisted van der Waals heterostructures based on high Tc superconductor Bi2Sr2CaCu2O8+δ lead to the realization of a high-temperature Josephson diode [2] for the first time. Such Josephson diodes offer an opportunity to engineer the current ph...

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...