arXiv subjects

Shaina Gandhi

Publications and source records attributed to Shaina Gandhi.

7 recordsLinked to original sources

arXiv2026

Sector-resolved non-Bloch topology and nonlocal entanglement dynamics in a bond-dissipative Kitaev chain

A core characteristic of dissipative non-Hermitian topology is that the relaxation dynamics tracks the non-Bloch bulk-boundary correspondence, rendering an algebraic decay in the gapless regime and an exponential falloff in the gapped phase, so that local observables directly diagnose the topology. We show that this correspondence breaks down in a dissipative topological superconductor, where the local observables turn blind to the very topology they are expected to decipher. Via a bond-dissipative dimerized Kitaev chain in a third-quantized rapidity-matrix formulation, we find that at zero chemical potential the Majorana rapidity matrix decomposes into two independent non-Hermitian sectors, each with its own generalized Brillouin zone and non-Bloch winding number, thereby revealing a sector-resolved non-Bloch bulk-boundary correspondence. The local density is a cross-sector covariance and relaxes at the sum of the two sector rates, so it remains sector-blind even when one sector is gapless and topological. For balanced gain and loss, the finite-time zero events of the entanglement spectrum under purely periodic-boundary Lindblad evolution recover this hidden edge content sector by sector, serving as a dynamical invariant that returns the open-boundary edge rapidities without physically opening the chain.

quant-ph↗

arXiv2026

Emergence of Non-Hermitian Magic Angles and Topological Phase Transitions in Twisted Bilayer $α$-$T_3$ Lattices

We investigate the flat-band properties and topological phase transitions in a non-Hermitian twisted bilayer $α-T_3$ lattice. Here, non-Hermiticity is introduced via Hatano-Nelson-type asymmetric hopping, while an aligned hexagonal boron nitride substrate provides a staggered sublattice mass to the system. We find that the introduction of non-reciprocal hopping splits the conventional single magic angle into three distinct non-Hermitian magic angles (NHMAs). Unlike the exceptional magic angles driven by spectral singularities, these NHMAs host perfectly isolated flat bands where the real and imaginary parts of the bandwidth simultaneously vanish. By mapping the complex eigenspectrum across the moiré Brillouin zone, we show that the scattered energy eigenvalues coalesce into well-defined, closed loop-like structures as the non-Hermitian parameter strength increases, indicating emergence of a nontrivial point-gap topology and hence the non-Hermitian skin effect. Furthermore, we characterize the topological phases by computing the direct band gap and the biorthogonal Chern number. While the system exhibits a transition to a higher topological phase at weak non-Hermiticity, we demonstrate that stronger non-Hermiticity drives the gap-closing boundaries to merge and their topological charges to mutually annihilate. This convergence results in a trivial gap closing and a complete suppression of the intermediate topological phase, confirming that non-Hermiticity fundamentally plays a crucial role with regard to destabilizing the robust topological features of this moiré system.

cond-mat.mes-hall↗

arXiv2025

Investigating topological in-gap states in non-Hermitian quasicrystal with unconventional $p$-wave pairing

The interplay of onsite quasiperiodic potential, superconductivity, and non-Hermiticity is explored in a non-Hermitian unconventional superconducting quasicrystal described by Aubry-André-Harper (NHAAH) model with $p$-wave pairing. In previous studies, the non-Hermiticity was only considered at the onsite quasiperiodic potential of the NHAAH model, and Majorana zero modes (MZMs) were observed under open boundary conditions (OBC) in this model. In this work, we study an NHAAH model with $p$-wave pairing, where non-Hermiticity is considered onsite by introducing complex quasiperiodic potential and asymmetry at the hopping part. Our analysis uncovers triple-phase transitions, where topological, metal-insulator, and unconventional real-to-complex transitions coincide at weak $p$-wave pairing strength. Additionally, instead of the MZMs observed in the symmetric hopping case, we observe the emergence of in-gap states under OBC in this model. These in-gap states are robust against disorder, underscoring their topological protection. Therefore, unlike the MZMs, which are very challenging to experimentally realize, these in-gap states can be used in topological quantum computational protocols.

cond-mat.dis-nn↗

arXiv2024

Superconducting $p$-wave pairing effects on one-dimensional non-Hermitian quasicrystals with power law hopping

We study the effects of superconducting $p$-wave pairing on the non-Hermitian Aubry-André-Harper model with power-law hopping. For the case of short-range hopping, weak pairing leads to oscillating quasi-Majorana zero modes, turning to edge-localized Majorana zero modes as pairing strength increases. For the case of long-range hopping, we observe the emergence of massive Dirac modes having oscillatory behavior, similar to Majorana modes with weak pairing. The massive Dirac modes localize at the edges as the pairing strength grows. The superconducting pairing spoils the plateaus observed in the fractal dimension of all the energy eigenstates of the Aubry-André-Harper model with power-law hopping. The number of plateaus decreases with the increasing pairing strength for the weak non-Hermiticity in the system. The phase diagram of the system reveals that real and complex energy spectrums correlate differently with the localization properties of the eigenstates depending on the strength of pairing and hopping range.

cond-mat.supr-con↗

arXiv2024

Transport properties in a two-dimensional Su-Schrieffer-Heeger model in Quantum Hall Regime

We investigate the transport properties of a two-dimensional Su-Schrieffer-Heeger (2D SSH) model in the quantum Hall regime using non-equilibrium Green's function formalism (NEGF). The device Hamiltonian, where the 2D SSH model serves as the channel, is constructed using a nearest-neighbor tight-binding model. The effect of an external perpendicular magnetic field is incorporated into the contacts via Peierls substitution. We observe a transition from a gapped phase to a flat band regime at zero energy by varying the magnetic field. This transition is characterized by the emergence of highly localized states in the bulk or edges, which we observe by calculating local density-of-states (LDOS). We analyze transport in the system along two directions ($x$ and $y$) via transmission measurements, indicating a magnetic field-induced transition from insulating to metallic phase. The study of the energy spectrum of the system shows the formation of Landau levels. Moreover, the quantum number of the non-degenerate and degenerate Landau levels (transmission modes) can be any integer or only an odd integer, depending on diagonal, inter-cell, and intra-cell hopping strengths. From the analysis of the transport properties along $y$-direction, we find that edge modes play a crucial role in facilitating ballistic transport.

cond-mat.mes-hall↗

arXiv2024

Non-Hermitian Aubry-André-Harper model with short- and long-range p-wave pairing

We investigate a non-Hermitian Aubry-André-Harper model with short-range, as well as long-range p-wave pairing. Here, the non-Hermiticity is introduced through the onsite potential. A comprehensive analysis of several critical aspects of this system is conducted, which includes eigenspectra, topological properties, localization properties, and the transition from real to complex energies. Specifically, we observe the emergence of Majorana zero modes in the case of short-range pairing, whereas massive Dirac modes emerge in the case of long-range pairing. More importantly, for the case of short-range pairing, we observe two simultaneous phase transitions or double phase transitions: topological and multifractal to localized phase. On the other hand, in the case of the long-range pairing, the topological and multifractal to localized transitions do not coincide. However, for both ranges of pairing, we identify a double phase transition where delocalized (or metallic) to a critical multifractal state is accompanied by an unconventional shift from real to complex energies. Unlike the short-range pairing case, we observe mobility edges in the long-range pairing case.

cond-mat.dis-nn↗

arXiv2023

Topological triple phase transition in non-Hermitian quasicrystals with complex asymmetric hopping

The triple phase transitions or simultaneous transitions of three different phases, namely topological, parity-time (PT) symmetry breaking, and metal-insulator transitions, are observed in an extension of PT symmetric non-Hermitian Aubry-André-Harper model. In this model, besides non-Hermitian complex quasi-periodic onsite potential, non-Hermiticity is also included in the nearest-neighbor hopping terms. Moreover, the nearest-neighbor hopping terms is also quasi-periodic. The presence of two non-Hermitian parameters, one from the onsite potential and another one from the hopping part, ensures PT symmetry transition in the system. In addition, tuning these two non-Hermitian parameters, we identify a parameters regime, where we observe the triple phase transition. Following some recent studies, an electrical circuit based experimental realization of this model is also discussed.

cond-mat.dis-nn↗