arXiv subjects

Binayyak B. Roy

Publications and source records attributed to Binayyak B. Roy.

5 recordsLinked to original sources

arXiv2026

Chiral Anomaly Induced Transverse Planar Transport Phenomena in Three Dimensional Spin-Orbit Coupled Metals

We investigate linear and nonlinear transverse planar transport phenomena (viz. linear and nonlinear Hall and Nernst coefficients) induced by chiral anomaly in three-dimensional spin-orbit coupled metallic systems. Unlike Weyl semimetals, these systems do not possess multiple Weyl nodes located at isolated points in the momentum space but instead host a pair of Fermi surfaces characterized by opposite Berry curvature fluxes enclosing the same band-degeneracy point. Using semiclassical Boltzmann transport formalism within the relaxation time approximation, we derive first- and second-order transverse planar transport coefficients induced by electrical and thermal gradients in the presence of an in-plane magnetic field. Our analysis reveals distinctive angular dependencies of the transport coefficients, along with characteristic scaling behavior with the magnetic field strength. Furthermore, we demonstrate that the anomaly-induced transport coefficients exhibit an exponential temperature dependence. This unconventional behavior leads to the violations of the Mott relation at comparatively low temperatures, highlighting unique thermoelectric signatures that can be probed experimentally in 3D spin-orbit coupled metallic systems.

cond-mat.mes-hall↗

arXiv2026

Quantum Inductance as a Phase-Sensitive Probe of Fermion Parity Switching in Majorana Nanowires

We study the flux-dependent quantum inductance of a one-dimensional (1D) semiconductor-superconductor (SM-SC) Majorana nanowire coupled to a quantum dot in an interferometric setup. Although quantum capacitance in this setup enables fast fermion parity readout, as has been demonstrated experimentally, it cannot by itself reliably confirm a protected fermion parity switch, a key signature of non-trivial topology and the existence of Majorana zero modes (MZMs). In realistic devices, disorder can produce avoided crossings or narrow double crossings between the two parity sectors that can mimic the behavior of a protected single parity switching, leading to false positives for non-trivial topological behavior. We show that quantum inductance provides a complementary probe that is directly sensitive to the phase structure of the low energy spectrum, allowing us to distinguish genuine fermion-parity crossings from avoided crossings or narrow double crossings. Using a general Lehmann framework applied to both effective models and full microscopic simulations with disorder, we demonstrate that only a true fermion-parity switch produces the characteristic inductive response of a protected crossing. In contrast, topologically trivial avoided crossings or narrow double crossings yield quantum inductance signatures that are markedly different from those of topologically nontrivial fermion parity crossings. Therefore, our results show that combined measurements of quantum capacitance and quantum inductance provide a robust and experimentally accessible means to identify true fermion-parity switches, corresponding to a nontrivial Pfaffian invariant.

cond-mat.mes-hall↗

arXiv2026

Pfaffian-based topological invariants for one dimensional semiconductor-superconductor heterostructures

We review the Pfaffian-based $\mathbb{Z}_2$ topological invariants in one dimensional semiconductor-superconductor (SM-SC) nanowire heterostructures and clarify their validity in finite and disordered systems. For the clean nanowire, the product of the Pfaffians of the Hamiltonian at particle-hole symmetric momenta $k=0,π$ changes sign at the topological phase transition defined by the bulk gap closing, leading to the definition of $\mathbb{Z}_2$ Kitaev invariant also known as Majorana number. We show that this momentum-space invariant is equivalent to a real space construction based on twisted boundary conditions, in which the sign of the product of the Pfaffians of the Hamiltonian under periodic and anti-periodic boundary conditions defines the $\mathbb{Z}_2$ index. By introducing a superlattice description of periodically repeated disorder, we demonstrate that the real space Pfaffian invariant defined as the sign of the Pfaffians of the Hamiltonian with periodic and anti-periodic boundary conditions, remains a well defined invariant even in the absence of microscopic translational symmetry. Within this framework, it is also equivalent to the recently defined periodic disorder invariant (PDI), which constitutes an integer valued ($\mathbb{Z}$) topological invariant in the presence of chiral symmetry. Finally, we prove that the sign of the Pfaffian of a quadratic Hamiltonian equals the fermion parity of its ground state, establishing a direct physical interpretation of the invariant, in terms of sign of the product of the ground state fermion parity with periodic and anti-periodic boundary conditions. Numerical results confirm the correspondence between sign of the Pfaffian reversals, flux-induced level crossings, and ground-state parity switching in clean and disordered nanowires.

cond-mat.mes-hall↗

arXiv2025

Topological invariant for finite systems in the presence of disorder

Topological invariants, rigorously defined only in the thermodynamic limit, have been generalized to topological indicators applicable to finite-size disordered systems. However, in many experimentally relevant situations, such as semiconductor-superconductor (SM-SC) hybrid nanowires hosting Majorana zero modes, the interplay between strong disorder and finite-size effects renders these indicators (e.g., the so-called topological visibility) biased and ill-defined, significantly limiting their usefulness. In this paper, we propose the topological invariant rigorously defined for an infinite system constructed by periodically repeating the original finite disordered system, as a topological indicator. Using the one-dimensional SM-SC hybrid nanowire as an example, we show that this general and transparent approach yields faithful topological indicators free from the biases affecting commonly used finite-size indicators, capturing the nature (topological or trivial) of the phase at generic points in parameter space, and providing a reliable tool for interpreting experimental results.

cond-mat.mes-hall↗

arXiv2024

Stabilizing topological superconductivity in disordered spin-orbit coupled semiconductor-superconductor heterostructures

We investigate theoretically a one-dimensional semiconductor-superconductor (SM-SC) heterostructure with Rashba spin-orbit coupling and parallel Zeeman field in the presence of disorder generated by random charged impurities and identify the optimal regimes for realizing topological superconductivity and Majorana zero modes. Using a Green's function approach, we show that upon increasing the disorder strength the stable topological superconducting phase characterized by robust end-to-end Majorana correlations "migrates" toward larger values of the Zeeman field and can be stabilized by increasing the effective SM-SC coupling. Based on these findings, we propose a strategy for accessing a regime characterized by well-separated Majorana zero modes that is based on (a) enhancing the strength of the effective SM-SC coupling (e.g., through interface engineering) and (b) expanding the range of accessible Zeeman fields (e.g., by enhancing the gyromagnetic ratio or optimizing the parent superconductor, to enable the application of larger magnetic fields). While this strategy may still require some reduction of the disorder strength, this requirement is significantly less strict than the corresponding requirement in a strategy that focuses exclusively on disorder reduction.

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