Kondo Effect in the Presence of Spin-Orbit Coupling

TL;DR

This paper investigates how spin-orbit coupling affects the Kondo effect in noncentrosymmetric superconductors, revealing a reduction and potential collapse of the Kondo temperature as spin-orbit interaction increases.

Contribution

It provides a theoretical analysis of the single-impurity Kondo problem incorporating spin-orbit coupling, showing its impact on the Kondo temperature and electron scattering.

Findings

Kondo temperature decreases with increasing spin-orbit coupling.

Strong spin-orbit coupling can cause a Kondo collapse.

Spin-orbit interaction conceals the typical log T resistivity dependence.

Abstract

Recently, a series of noncentrosymmetric superconductors has been a subject of considerable interest since the discovery of superconductivity in CePt_3Si. In noncentrosymmetric materials, the degeneracy of bands is lifted in the presence of spin-orbit coupling. This will bring about new effects in the Kondo effect since the band degeneracy plays an important role in the scattering of electrons by localized spins. We investigate the single-impurity Kondo problem in the presence of spin-orbit coupling. We examine the effect of spin-orbit coupling on the scattering of conduction electrons, by using the Green's function method, for the s-d Hamiltonian, with employing a decoupling procedure. As a result, we obtain a closed system of equations of Green's functions, from which we can calculate physical quantities. The Kondo temperature T_K is estimated from a singularity of Green's functions. We show that T_K is reduced as the spin-orbit coupling constant \alpha is increased. When 2\alpha k_F is comparable to or greater than k_BT_K(\alpha=0), T_K shows an abrupt decrease as a result of the band splitting. This suggests a Kondo collapse accompanied with a sharp decrease of T_K. The log T-dependence of the resistivity will be concealed by the spin-orbit interaction.