arXiv subjects

Bijay Kumar Sahoo

Publications and source records attributed to Bijay Kumar Sahoo.

6 recordsLinked to original sources

arXiv2026

Nonreciprocal transverse currents in Rashba metal junctions under out-of-plane Zeeman fields

We study charge transport across a junction between a normal metal and a Rashba metal in the presence of a Zeeman field applied to the spin--orbit coupled region. While an out-of-plane Zeeman field does not generate a transverse response in a homogeneous Rashba system, we show that such a junction exhibits a finite transverse conductivity that is inherently nonreciprocal, i.e., it depends on the direction of the applied bias. We demonstrate that this effect originates from the breaking of the $k_y \to -k_y$ symmetry of the Hamiltonian in the presence of the Zeeman field, which prevents cancellation of transverse current contributions from opposite transverse momenta. We further show that evanescent modes in the spin--orbit coupled region play a crucial role by carrying a finite spin polarization that gives rise to a transverse current localized near the junction. The transverse conductivity exhibits a peak at an energy scale set by the Zeeman field, displays distinct behavior for opposite bias directions, and shows spatial dependence governed by the nature of the contributing modes. We also identify bound states at the junction for attractive barrier strengths, which enhance conductivity when their energies lie near the transport window. Our results reveal a mechanism for nonreciprocal transverse charge transport in Rashba systems without requiring in-plane magnetic fields or ferromagnetic contacts, and should be experimentally accessible in semiconductor heterostructures.

cond-mat.mes-hall↗

arXiv2025

Giant field-free transverse Josephson diode effect in altermagnets

We predict a field-free transverse Josephson diode effect in altermagnets (AMs) with Rashba spin--orbit coupling, achieving diode efficiencies exceeding $3000\%$ and unidirectional transverse supercurrents in four-terminal junctions. In this geometry, a longitudinal phase bias generates transverse supercurrents that exhibit nonreciprocity and a finite anomalous phase shift, while the longitudinal current itself displays a Josephson diode effect. Both responses are tunable via the N\'eel vector orientation. We further show that the effect remains robust against moderate disorder and imperfect interfaces. These results establish AMs as a promising platform for nonreciprocal superconducting transport, with clear routes toward experimental realization.

cond-mat.mes-hall↗

arXiv2025

Four-terminal Josephson junctions: diode effects, anomalous currents and transverse currents

We study a multi-terminal Josephson junction consisting of a central spin-orbit-coupled (SOC) region with an in-plane Zeeman field connected to four superconducting terminals. This setup allows for the simultaneous measurement of both longitudinal and transverse Josephson currents in response to a phase bias and provides a platform to probe the planar Hall effect in superconducting transport. We find that the system exhibits anomalous Josephson effect (AJE) and Josephson diode effect (JDE) when the symmetry between opposite momentum modes is broken in SOC region. Specifically, breaking the symmetry between $k_x$ and $-k_x$ results in JDE and AJE in the longitudinal Josephson current, while breaking the symmetry between $k_y$ and $-k_y$ leads to a finite transverse Josephson current that also exhibits JDE and AJE. Transverse Josephson diode effect coefficient attains values as large as $500\%$ for realistic set of parameters. Furthermore, for specific parameter choices, the current-phase relation in the transverse direction supports unidirectional transport, highlighting its potential for superconducting circuit applications. Our setup offers a new route to engineering nonreciprocal superconducting transport.

cond-mat.supr-con↗

arXiv2024

Persistent currents in mesoscopic spin-orbit coupled rings due to an applied Zeeman field

Persistent currents (PCs) in mesoscopic rings have been a subject of intense investigation since their proposal by Büttiker, Landauer, and Imry in 1983. In this paper, we explore the behavior of PC in spin-orbit coupled rings under the influence of a Zeeman field (without a need for a flux threading the ring), contrasting it with traditional PC observed in rings threaded by magnetic flux. Our study reveals that the emergence of PC in our setup crucially depends on nonzero values of spin-orbit coupling and the Zeeman field. Through theoretical analysis and numerical calculations, we uncover several intriguing phenomena. Specifically, in ballistic rings, we observe an inverse proportionality between PC and system size, with PC being zero at half filling for even numbers of sites. Additionally, the introduction of on-site disorder leads to the suppression of PC, with exponential decay observed for large disorder strengths and quadratic decay for smaller disorder strengths. Notably, disorder can enhance PC in individual samples, albeit with a configuration-averaged PC of zero. Furthermore, we find that the standard deviation of PC increases with disorder strength, reaching a maximum before decreasing to zero at high disorder strengths. We study the case of PC when the Zeeman field and the spin-orbit field are noncollinear. We also study persistent spin current which shows behavior similar to that of PC except that at half filling, it is not zero. Our findings shed light on the intricate interplay between spin-orbit coupling, Zeeman fields, and disorder in mesoscopic quantum systems, offering new avenues for theoretical exploration and experimental verification.

cond-mat.mes-hall↗

arXiv2023

Transverse currents in spin transistors

In many systems, planar Hall effect wherein transverse signal appears in response to longitudinal stimulus is rooted in spin-orbit coupling. A spin transistor put forward by Datta and Das on the other hand consists of ferromagnetic leads connected to spin-orbit coupled central region and its conductance can be controlled by tuning the strength of spin-orbit coupling. We find that transverse currents also appear in Datta-Das transistors made by connecting two two-dimensional ferromagnetic reservoirs to a central spin-orbit coupled two-dimensional electron gas. We find that the spin transistor exhibits a nonzero transverse conductivity which depends on the direction of polarization in ferromagnets and the location where it is measured. We study the conductivities for the system with finite and infinite widths. The conductivities exhibit Fabry-Pérot type oscillations as the length of the spin-orbit coupled regions is varied. Interestingly, even in the limit when longitudinal conductivity is made zero by cutting off the junction between the central spin-orbit coupled region and the ferromagnetic lead on one side (right), the transverse conductivities remain nonzero in the regions that are on the left side of the cut-off junction.

cond-mat.mes-hall↗

arXiv2011

Effect of Piezoelectric Polarization on Phonon group velocity in Wurtzite Nitrides

We have investigated the effect of piezoelectric (PZ) polarization property on group velocity of phonons in binary as well as in ternary wurtzite nitrides. It is found that with the presence of PZ polarization property, the phonon group velocity is modified. The change in phonon group velocity due to PZ polarization effect directly depends on piezoelectric tensor value. Using different piezoelectric tensor values recommended by different workers in the literature, percent change in group velocities of phonons has been estimated. The Debye temperatures and frequencies of binary nitrides GaN, AlN and InN are also calculated using the modified group velocities. For ternary nitrides AlxGa(1-x)N, InxGa(1-x)N and InxAl(1-x)N, the phonon group velocities have been calculated as a functions of composition. A small positive bowing is observed in phonon group velocities of ternary alloys. Percent variations in phonon group velocities are also calculated for a straightforward comparison among ternary nitrides. The results are expected to show a change in phonon relaxation rates and thermal conductivity of III-nitrides when piezoelectric polarization property is taken into account.

cond-mat.mtrl-sci↗