arXiv subjects

Debottam Mandal

Publications and source records attributed to Debottam Mandal.

6 recordsLinked to original sources

arXiv2026

Quantum metric quadrupoles in elemental bismuth thin films

The nonlinear transport properties of solids are deeply rooted in the quantum geometry of their electronic wavefunctions, which is encoded in the quantum geometric tensor. Its real part, known as the quantum metric, has been recently identified as a primary origin of nonlinear transport in quantum materials where time-reversal and inversion symmetries are not simultaneously present. Consequently, the influence of the quantum metric on the largest class of materials -- non-magnetic and centrosymmetric systems -- has remained entirely elusive. Here, we demonstrate that third-order transport in centrosymmetric materials hosting relativistic fermions is governed by quantum metric quadrupoles (QMQs). We show that these QMQs can originate from both the non-Abelian quantum geometry of bulk three-dimensional Dirac fermions and the Abelian quantum geometry of spin-orbit-coupled surface states. In stark contrast to all zero-field nonlinear transport signatures known to date, the current driven by these QMQs persists as a robust, non-vanishing observable even in highly scalable polycrystalline thin films. We experimentally validate this quantum metric footprint by measuring nonlinear transport in thin films of elemental bismuth, observing a robust, surface-dominated, and broadband third-harmonic generation that persists up to room temperature. Our findings uncover a hidden role of the quantum metric in polycrystalline systems, establishing third-order nonlinear transport as a high-precision diagnostic tool of wavefunction geometry under ambient conditions.

cond-mat.mes-hall↗

arXiv2025

Band Geometry Induced Third-Harmonic Generation

Third-harmonic generation (THG) is a key nonlinear optical process for ultrafast imaging, terahertz (THz) signal generation, and symmetry-sensitive probes, often dominating in centrosymmetric materials where lower-order responses vanish. Yet, the role of band geometry, Fermi surface effects, and disorder in enabling large and tunable THG remains poorly understood. Here, we develop a finite-frequency quantum kinetic theory of THG based on the density matrix formalism, deriving the third-harmonic conductivity tensor. Our framework isolates five distinct band-geometric contributions to interband and intraband processes, separates Fermi sea from Fermi surface terms, and incorporates disorder effects phenomenologically. We further provide a complete symmetry classification of THG for all 122 magnetic point groups. Applying the theory to the spin-split altermagnet RuO$_2$, we trace its THG response to specific geometric terms. These results establish a predictive foundation for designing materials with enhanced and tunable THG in the finite-frequency regime.

physics.optics↗

arXiv2024

Light-induced Nonlinear Resonant Spin Magnetization

The optical generation of nonequilibrium spin magnetization plays a crucial role in advancing spintronics, providing ultrafast control of magnetization dynamics without the need for magnetic fields. Here, we demonstrate the feasibility of light-induced nonlinear spin magnetization (LNSM), which becomes a dominant effect in centrosymmetric materials. We reveal the quantum geometric origins of various LNSM contributions in both metallic and insulating systems. Through detailed symmetry analysis, we predict significant LNSM in the antiferromagnetic material CuMnAs. Notably, under circularly polarized light, the spin magnetization exhibits helicity-dependent behavior, reversing with opposite light helicity. These findings open up new possibilities for generating LNSM-driven nonlinear spin-orbit torques and developing innovative opto-spintronic devices.

cond-mat.mes-hall↗

arXiv2023

Quantum Geometry Induced Third Order Nonlinear Transport Responses

Nonlinear transport phenomena offer an exciting probe into the band geometry and symmetry properties of a system. While most studies on nonlinear transport have looked at second-order nonreciprocal responses in noncentrosymmetric systems, the reciprocal third-order effects dominant in centrosymmetric systems remain largely uncharted. Here, we uncover two significant contributions to third-order charge conductivity: one affecting longitudinal resistance and another impacting the Hall effect. We demonstrate that these previously unexplored contributions arise in time-reversal symmetry-broken systems from band geometric quantities such as the Berry curvature and the symplectic connection. We prescribe a detailed symmetry dictionary to facilitate the discovery of these fundamental transport coefficients. Additionally, we unify our quantum kinetic results with the semiclassical wave-packet formalism to unveil all contributions to third-order charge transport. We illustrate our results in antiferromagnetic monolayer SrMnBi$_2$. Our comprehensive study significantly advances the fundamental understanding of reciprocal nonlinear responses.

cond-mat.mes-hall↗

arXiv2022

Nonlinear magnetotransport in Weyl semimetal

The recent discovery of the quantum nonlinear Hall effect has revived the field of nonlinear transport. Here, we predict magnetic field-induced nonlinear Hall effect in time-reversal symmetric Weyl semimetal. We show that the interplay of the band geometric quantities, such as the Berry curvature, and the magnetic part of the Lorentz force can give rise to finite nonlinear Hall conductivity that is linear in the magnetic field. Such nonlinear Hall conductivity can manifest through nonlinear transport measurement as well as nonlinear optical phenomena like photocurrent and the second harmonic generation.

cond-mat.mes-hall↗

arXiv2020

Magnus Nernst and thermal Hall effect

Motivated by the recent prediction of the Magnus Hall effect in systems with broken inversion symmetry, in this paper we study the Magnus Nernst effect and the Magnus thermal Hall effect. In presence of an in-built electric field, the self rotating wave-packets of electrons with finite Berry curvature generate a Magnus velocity perpendicular to both. This anomalous Magnus velocity gives rise to the Magnus Hall transport which manifests in all four electro-thermal transport coefficients. In this paper, we demonstrate the existence of the Magnus Nernst and Magnus thermal Hall effect in monolayer WTe2 and gapped bilayer graphene, using the semiclassical Boltzmann formalism. We show that the Magnus velocity can also give rise to Magnus valley Hall effect in gapped graphene. Magnus velocity can be useful for experimentally probing the Berry curvature, and design of novel electrical and electro-thermal devices.

cond-mat.mes-hall↗