Talks

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...

We propose an effective Hamiltonian approach to understand a variety of partially magnetically ordered phases in a Kondo lattice. Such partial order, where only selected sites are Kondo-screened while the others develop local moments, have been observed in many heavy-fermion compounds. The proposed effective Hamiltonian retains two important features of the fundamental Kondo-lattice model: (i) formation of a Kondo singlet leading to vanishing of the local magnetic moment, and (ii) spatially correlated nature of the electronic kinetic energy. The Hamiltonian belongs to a class of coupled classical-quantum models that can be reliably studied using hybrid Monte Carlo simulations. I will try to motivate the model and demonstrate the approach for the case of a square lattice where we unveil a number of magnetic phases with partial order. I will further motivate a fully classical spin model to describe the partial magnetic order in Kondo lattices.