arXiv subjects

Asimpunya Mitra

Publications and source records attributed to Asimpunya Mitra.

7 recordsLinked to original sources

arXiv2026

Chiral superconductors from parent states with nonuniform Berry curvature: Momentum-space vortices, Bogoliubov-de Gennes topology, and thermal Hall conductivity

We investigate chiral superconductivity emerging from parent electronic states with non-uniform Berry curvature, motivated by recent experiments in rhombohedral graphene multilayers. Using the continuum $λ_N$-model-a tunable platform with independently controllable Berry curvature profiles-we solve the full BCS gap equation on a continuum Chern band beyond the weak-coupling limit. We find that a non-uniform Berry curvature of the parent band enriches the superconducting order parameter, leading to the formation of momentum-space vortices in the gap function away from high-symmetry points. By tuning the Berry curvature profile, we identify distinct regimes associated with vortex nucleation and vortex number saturation, and show that the nucleation of momentum-space vortices tends to lower the condensation energy. We then show analytically that the parent band Chern number constrains the number of momentum-space vortices that can nucleate in the gap-independent of details of the $λ_N$-model. We also provide a gauge-invariant formulation for computing the Bogoliubov-de Gennes (BdG) Berry curvature for continuum models, and find that it is determined by a momentum-space phase current. The winding of this current around vortices in the occupied region in turn determines the BdG Chern number. Finally, we discuss how thermal Hall measurements can be used to probe the formation of momentum-space vortices. Our results highlight the crucial role of Berry curvature in shaping chiral superconductivity, and offer guiding principles for its identification in systems such as rhombohedral graphene.

cond-mat.supr-con↗

arXiv2026

Superconductivity in kagome metals due to soft loop-current fluctuations

We demonstrate that soft fluctuations of translation symmetry-breaking loop currents provide a mechanism for unconventional superconductivity in kagome metals that naturally addresses the multiple superconducting phases observed under pressure. Focusing on the rich multi-orbital character of these systems, we show that loop currents involving both vanadium and antimony orbitals generate low-energy collective modes that couple efficiently to electrons near the Fermi surface and mediate attractive interactions in two distinct unconventional pairing channels. While loop-current fluctuations confined to vanadium orbitals favor chiral $d+id$ superconductivity, which spontaneously breaks time-reversal symmetry, the inclusion of antimony orbitals stabilizes an $s^{\pm}$ state that is robust against disorder. We argue that these two states are realized experimentally as pressure increases and the antimony-dominated Fermi surface sheet undergoes a Lifshitz transition.

cond-mat.supr-con↗

arXiv2025

Quantum Spin Liquids in Weak Mott Insulators with a Spin-Orbit Coupling

The weak Mott insulating regime of the triangular lattice Hubbard model exhibits a rich magnetic phase diagram as a result of the ring exchange interaction in the spin Hamiltonian. These phases include the Kalmeyer-Laughlin type chiral spin liquid (CSL) and a valence bond solid (VBS). A natural question arises regarding the robustness of these phases in the presence of a weak spin-orbit coupling (SOC). In this study, we derive the effective spin model for the spin-orbit coupled triangular lattice Hubbard model in the weak Mott insulting regime, including all SOC-mediated spin-bilinears and ring-exchange interactions. We then construct a simplified spin model keeping only the most relevant SOC-mediated spin interactions. Using infinite density matrix renormalization group (iDMRG) we show that the CSL and VBS phases of the triangular lattice Hubbard model can be stabilized in the presence of a weak SOC. The stabilization results from a compensation between the Dzyaloshinskii-Moriya interaction and a SOC-mediated ring exchange interaction. We also provide additional qualitative arguments to intuitively understand the compensation mechanism in the iDMRG quantum phase diagrams. This mechanism for stabilization can potentially be useful for the experimental realization of quantum spin liquids.

cond-mat.str-el↗

arXiv2025

Interplay of competing bond-order and loop-current fluctuations as a possible mechanism for superconductivity in kagome metals

The pairing symmetry and underlying mechanism for superconducting state of AV${}_3$Sb${}_5$ (A=K, Rb, Cs) kagome metal has been a topic of intense investigation. In this work, we consider an 8-band minimal model, which includes V, and the two types of Sb, both within and above/below the kagome plane. This model captures the Fermi surface pocket with significant in-plane Sb contribution near the zone center, and also has the two types of van Hove singularities (VHS), one of which has a strong out of plane Sb weight. By including V-V and V-planar Sb nearest-neighbor Coulomb interactions, we obtain the susceptibilities for fluctuating bond-order and loop-current in both charge and spin channels, and examine the resulting superconducting instabilities. In particular, we find that the time-reversal odd (even) charge-loop-current (charge bond-order) fluctuations favor unconventional (conventional) pairing symmetry such as $s_{+-}$ and $d+id$ ($s_{++}$). Recent experimental works have highlighted the presence of $s$-wave pairing with two distinct gaps, one isotropic and one anisotropic. We discuss how this scenario may be compatible with either $s_{++}$ or $s_{+-}$ pairing, with an isotropic gap on the pocket dominated by in-plane Sb, but a highly anisotropic gap on V-dominated bands.

cond-mat.supr-con↗

arXiv2024

Scalable simulation of non-equilibrium quantum dynamics via classically optimised unitary circuits

The advent of near-term digital quantum computers could offer us an exciting opportunity to investigate quantum many-body phenomena beyond that of classical computing. To make the best use of the hardware available, it is paramount that we have methods that accurately simulate Hamiltonian dynamics for limited circuit depths. In this paper, we propose a method to classically optimise unitary brickwall circuits to approximate quantum time evolution operators. Our method is scalable in system size through the use of tensor networks. We demonstrate that, for various three-body Hamiltonians, our approach produces quantum circuits that can outperform Trotterization in both their accuracy and the quantum circuit depth needed to implement the dynamics, with the exact details being dependent on the Hamiltonian. We also explain how to choose an optimal time step that minimises the combined errors of the quantum device and the brickwall circuit approximation.

quant-ph↗

arXiv2024

Quantum Fluctuations Suppress the Critical Fields in BaCo$_2$(AsO$_4$)$_2$

Early efforts to realize exotic quantum ground states in frustrated magnets focused on frustration arising from the lattice geometry alone. Attention has shifted to bond-dependent anisotropic interactions, as well as further-neighbor interactions, on non-geometrically-frustrated lattices due to their greater versatility. The honeycomb magnet BaCo$_2$(AsO$_4$)$_2$ recently emerged as a candidate host for both bond-dependent (e.g. Kitaev) and third-neighbor ($J_3$) interactions, and has become a model experimental system due to its relatively low levels of disorder. Understanding the relative importance of different exchange interactions holds the key to achieving novel ground states, such as quantum spin liquids. Here, we use the magnetotropic susceptibility to map out the intermediate and high-field phase diagram of BaCo$_2$(AsO$_4$)$_2$ as a function of the out-of-plane magnetic field direction at $T = 1.6$ K. We show that the experimental data are qualitatively consistent with classical Monte Carlo results of the XXZ-$J_1$-$J_3$ model with small Kitaev and off-diagonal exchange couplings included. However, the calculated critical fields are systematically larger than the experimental values. Infinite-DMRG computations on the quantum model reveal that quantum corrections from a nearby ferromagnetic state are likely responsible for the suppressed critical fields. Together, our experiment and theory analyses demonstrate that, while quantum fluctuations play an important role in determining the phase diagram, most of the physics of BaCo$_2$(AsO$_4$)$_2$ can be understood in terms of the classical dynamics of long-range ordered states, leaving little room for the possibility of a quantum spin liquid.

cond-mat.str-el↗

arXiv2021

Magnon Interference Tunneling Spectroscopy as a Probe of 2D Magnetism

Probing two-dimensional single-layer quantum magnets remains a significant challenge. In this letter, we propose exploiting tunneling spectroscopy in the presence of magnetic impurities to obtain information about the magnon dispersion relations in analogy to quasiparticle interference in non-magnetic materials. We show this technique can be used to establish the dispersion relations even for frustrated magnets, where the presence of an impurity generally leads to a nontrivial spin texture. Finally, we consider the problem of establishing Chern magnon bands in 2D magnets showing how tuneable impurities allow probing the nature of the surface states.

cond-mat.mes-hall↗