Circular current in a one-dimensional open quantum ring in the presence of magnetic field and spin-orbit interaction

TL;DR

This paper investigates how magnetic field and spin-orbit interaction influence circular and transport currents in an open quantum ring, revealing symmetry-breaking effects that enable control of charge and spin currents for spintronic applications.

Contribution

It provides a detailed analysis of symmetry-breaking effects on current densities and degeneracy lifting in quantum rings with magnetic field and spin-orbit interaction.

Findings

Symmetry breaking affects circular current density spectra.

Charge and spin current densities respond differently to symmetry breaking.

Transmission function remains symmetric around zero energy despite symmetry breaking.

Abstract

In an open quantum system having a channel in the form of loop geometry, the current inside the channel, namely circular current, and overall junction current, namely transport current, can be different. A quantum ring has doubly degenerate eigen energies due to periodic boundary condition that is broken in an asymmetric ring where the ring is asymmetrically connected to the external electrodes. Kramers' degeneracy and spin degeneracy can be lifted by considering non-zero magnetic field and spin-orbit interaction (SOI), respectively. Here, we find that symmetry breaking impacts the circular current density vs energy ($E$) spectra in addition to lifting the degeneracy. For charge and spin current densities, the corresponding effects are not the same. Under symmetry-breaking they may remain symmetric or anti-symmetric or asymmetric around $E = 0$ whereas the transmission function (which is proportional to the junction current density) vs energy characteristic remains symmetric around $E = 0$. This study leads us to estimate the qualitative nature of the circular current and the choices of Fermi-energy/chemical potential to have a net non-zero current. As a result, we may manipulate the system to generate pure currents of charge, spin, or both, which is necessary for any spintronic and electronic applications.