arXiv subjects

Gaurab Kumar Dash

Publications and source records attributed to Gaurab Kumar Dash.

5 recordsLinked to original sources

arXiv2026

Floquet Majorana flat bands and emergent Cooper pair symmetries in $p-$wave magnet$-$superconductor heterostructure

We investigate the emergence of topological superconductivity at the two-dimensional heterostructure interface between a $p$-wave magnet (pWM) and an $s$-wave superconductor. By analyzing nodal gap closings, we identify seven distinct nodal topological phases, each characterized by the presence of Majorana zero-energy flat bands and quantized zero-bias conductance peaks. We demonstrate that the effective $p$-wave nature of the system gives rise to spin-triplet pairing correlations with even-frequency, odd-parity and odd-frequency, even-parity symmetries. Notably, the introduction of inter-orbital hopping induces an exotic orbital-singlet term characterized by simultaneous odd-parity and odd-frequency. Furthermore, we explore the transition from static phases to Floquet topological regimes through periodic driving. These driven phases host both zero and $\pi$ Majorana flat bands, with transport signatures governed by the Floquet sum rule. Most significantly, we show that periodic driving fundamentally reshapes the topological and superconducting landscape by generating multiple nodal points that support higher winding numbers and multiple Majorana flat bands, while the emergent Floquet degree of freedom doubles the number of symmetry-allowed Cooper-pair correlations. The first class of correlations is hosted by the even-Floquet sectors and has a direct counterpart in the static limit. In contrast, the second is a distinct Floquet-generated class that confines to the odd-Floquet sectors, representing a fundamentally nonequilibrium pairing channel that cannot exist in static systems. Finally, we demonstrate the robustness of these topological modes against strong disorder, confirming their potential for stable fault-tolerant applications.

cond-mat.mes-hall↗

arXiv2025

Floquet multiple exceptional points with higher-order skin effect

We investigate the rich non-equilibrium physics arising in periodically driven open quantum systems, specifically those realized within microcavity resonators, whose dynamics are governed by a non-Hermitian Hamiltonian hosting Floquet Exceptional Points (FEPs). By introducing a periodically quenched driving protocol, we analytically derive the Floquet effective Hamiltonian and determine the locations of multiple FEPs harbored within the Floquet bulk bands. We demonstrate that the pair-production and annihilation of these FEPs can be precisely controlled by fine-tuning the system parameters, and zero and $\pi$ FEPs are topologically characterized by robust integer quantized winding numbers. To probe these singularities, we introduce a bi-orthogonal Floquet fidelity susceptibility, whose value exhibits large non-zero peaks at the momentum points hosting FEPs in the Brillouin zone. Furthermore, the momentum-summed susceptibility displays a sharp divergence when the number of FEPs change with respect to the time period of the drive. Our findings also reveal the emergence of Floquet edge states around zero energy and Dirac-like dispersion around $\pi$. Moreover, our model reveals a higher-order skin effect, where the periodically driven Hamiltonian hosts skin modes localized at both edges and corners. These insights offer novel avenues for the Floquet engineering of topological singularities in driven dissipative systems, with significant potential for manipulating light and matter at the microscale.

cond-mat.mes-hall↗

arXiv2024

Fingerprint of Non-Hermiticity in d-wave Altermagnet

We develop the non-Hermitian counterpart of a new class of collinear magnets, dubbed altermagnets, delineated by net zero magnetization with momentum-dependent spin-splitting bands. The application of an imaginary gauge field in a two-dimensional $d$-wave altermagnet injects a non-reciprocal intercell hopping without hosting exceptional points (EPs). This non-Hermitian phase hosts a point gap which remains robust in the presence and absence of Rashba spin-orbit coupling. By attaching a ferromagnetic lead with the altermagnet, we uncover the emergence of two pairs of second-order EPs. We establish that each of the EPs is associated with a half-integer quantized topological charge, a hallmark signature of the non-Hermitian topology. The existence of this non-Hermitian exceptional phase has been further confirmed by linear variation with the respective momentum and coalescence of the spin expectation value at the EPs. Finally, we demonstrate that the application of a planar magnetic field to the junction not only tunes the location of the EPs but also can annihilate a single pair or even all pairs of EPs with opposite topological charges depending upon the field strength and direction.

cond-mat.mes-hall↗

arXiv2023

Floquet Exceptional Topological Insulator

We propose a novel way of modulating exceptional topology by implementing Floquet engineering in non-hermitian (NH) systems. We introduce Floquet exceptional topological insulator which results from shining light on a conventional three-dimensional NH topological insulator. Lightmatter interaction facilitates the quantum phases of matter to exhibit a novel phenomenon, where, the point gaps in the bulk host surface states. These distinct surface states either fill the point gap in the complex eigenspectrum or exhibit exceptional points in the presence of a magnetic field. We also highlight the existence of a quantum anomaly generated by photo-induced modulation. The existence of the Floquet biorthogonal Chern number and spectral winding number show that the momentum slices exhibit NH skin effect, even though the system as a whole does not. We also employ wave-dynamics evolution to illustrate the NH surface skin effect.

cond-mat.mes-hall↗

arXiv2022

Non-Hermitian higher-Order Weyl semimetal with surface diabolic points

Higher-order topology in non-Hermitian (NH) systems has recently become one of the most promising and rapidly developing fields in condensed matter physics. Many distinct phases that were not present in the Hermitian equivalents are shown in these systems. In this work, we examine how higher-order Weyl semimetals are impacted by NH perturbation. We identify a new type of topological semimetal, i.e., non-Hermitian higher-order Weyl semimetal (NHHOWS) with surface diabolic points. We demonstrate that in such an NHHOWS, new exceptional points inside the bulk can be created and annihilated, therefore allowing us to manipulate their number. At the boundary, these exceptional points are connected through unique surface states with diabolic points and hinge states. For specific system parameters, the surface of NHHOWS behaves as a Dirac phase with linear dispersion or a Luttinger phase with a quadratic dispersion, thus paving a way for Dirac-Luttinger switching. Finally, we employ the biorthogonal technique to reinstate the standard bulk boundary correspondence for NH systems and compute the topological invariants. The obtained quantized biorthogonal Chern number and quadruple moment topologically protect the unique surface and hinge states, respectively.

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