Josephson diode effect in one-dimensional quantum wires connected to superconductors with mixed singlet-triplet pairing.

The Josephson diode effect (JDE), characterized by asymmetric critical currents in a Josephson junction, has drawn considerable attention in the field of condensed matter physics. We investigate the conditions under which JDE can manifest in a one-dimensional Josephson junction composed of a spin-orbit-coupled quantum wire with an applied Zeeman field, connected between two superconductors (SCs). Our study reveals that while spin-orbit coupling (SOC) and a Zeeman field in the quantum wire are not sufficient to induce JDE when the SCs are purely singlet, introduction of triplet pairing in the SCs leads to the emergence of JDE.

Majorana fermions in Kitaev chains side-coupled to normal metals.

Majorana fermions, exotic particles with potential applications in quantum computing, have garnered significant interest in condensed matter physics. The Kitaev model serves as a fundamental framework for investigating the emergence of Majorana fermions in one-dimensional systems. We explore the intriguing question of whether Majorana fermions can arise in a normal metal (NM) side-coupled to a Kitaev chain (KC) in the topologically trivial phase.

Josephson diode effect in junctions of superconductors with band asymmetric metals.

At interfaces connecting two superconductors (SCs) separated by a metallic layer, an electric current is induced when there is a disparity in the phases of the two superconductors. We elucidate this phenomenon based on the weights of the Andreev bound states associated with the states carrying currents in forward and reverse directions. Typically, current phase relation (CPR) in Josephson junctions is an odd function.

Transport across junctions of altermagnets with normal metals and ferromagnets.

Altermagnet (AM) is a novel time reversal symmetry broken magnetic phase with-wave order which has been experimentally realized recently. We discuss theoretical models of AM based systems on lattice and in continuum. We show equivalence between the lattice and continuum models by mapping the respective parameters.

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 (SOC). A spin transistor put forward by Datta and Das on the other hand consists of ferromagnetic leads connected to SOC central region and its conductance can be controlled by tuning the strength of SOC. We find that transverse currents also appear in Datta-Das transistors made by connecting two two-dimensional ferromagnetic reservoirs to a central SOC two-dimensional electron gas.

Transmission across non-HermitianPT-symmetric quantum dots and ladders.

A non-Hermitian (NH) region connected to semi-infinite Hermitian lattices acts either as a source or as a sink and the probability current is not conserved in a scattering typically. Even aPT-symmetric region that contains both a source and a sink does not lead to current conservation plainly. We propose a model and study the scattering across a NHPT-symmetric two-level quantum dot (QD) connected to two semi-infinite one-dimensional lattices in a special way so that the probability current is conserved.

Finite transverse conductance and anisotropic magnetoconductance under an applied in-plane magnetic field in two-dimensional electron gases with strong spin-orbit coupling.

The current in response to a bias in certain two-dimensional electron gas (2DEG), can have a nonzero transverse component under a finite magnetic field applied in the plane where electrons are confined. This phenomenon known as planar Hall effect (PHE) is accompanied by dependencies of both the longitudinal and the transverse components of the current on the anglebetween the bias direction and the magnetic field. This effect can be observed in a variety of systems, for example in topological insulators where spin-momentum locking of the topologically protected surface states is the root cause for the effect and in magnetic systems where anisotropic magnetic ordering induces it.

Finite transverse conductance in topological insulators under an applied in-plane magnetic field.

Recently, in topological insulators (TIs) the phenomenon of planar Hall effect wherein a current driven in presence an in-plane magnetic field generates a transverse voltage has been experimentally witnessed. There have been a couple of theoretical explanations of this phenomenon. We investigate this phenomenon based on scattering theory on a normal metal (NM)-TI-normal metal hybrid structure and calculate the conductances in longitudinal and transverse directions to the applied bias.

Nonadiabatic charge pumping across two superconductors connected through a normal metal region by periodically driven potentials.

Periodically driven systems exhibit resonance when the difference between an excited state energy and the ground state energy is an integer multiple oftimes the driving frequency. On the other hand, when a superconducting phase difference is maintained between two superconductors, subgap states appear which carry a Josephson current. A driven Josephson junction therefore opens up an interesting avenue where the excitations due to applied driving affect the current flowing from one superconductor to the other.

Transconductance as a probe of nonlocality of Majorana fermions.

Each end of a Kitaev chain in topological phase hosts a Majorana fermion. Zero bias conductance peak is an evidence of Majorana fermion when the two Majorana fermions are decoupled. These two Majorana fermions are separated in space and this nonlocal aspect can be probed when the two are coupled.

Enhancement of crossed Andreev reflection in a Kitaev ladder connected to normal metal leads.

We study nonlocal transport in a two-leg Kitaev ladder connected to two normal metals. The coupling between the two legs of the ladder when the legs are maintained at a (large) superconducting phase difference, results in the creation of subgap Andreev states. These states in turn are responsible for the enhancement of crossed Andreev reflection (CAR).

Edge states of a three-dimensional topological insulator.

We use the bulk Hamiltonian for a three-dimensional topological insulator such as Bi(2) Se(3) to study the states which appear on its various surfaces and along the edge between two surfaces. We use both analytical methods based on the surface Hamiltonians (which are derived from the bulk Hamiltonian) and numerical methods based on a lattice discretization of the bulk Hamiltonian. We find that the application of a potential barrier along an edge can give rise to states localized at that edge.