Anisotropic Kondo screening induced by spin-orbit coupling in quantum wires

TL;DR

This study uses numerical renormalization group methods to explore how spin-orbit coupling induces anisotropic Kondo screening in quantum wires, revealing field-direction dependent impurity properties and potential for measuring SOC strength ratios.

Contribution

It provides the first detailed analysis of anisotropic Kondo effects induced by spin-orbit coupling in quantum wires with external magnetic fields.

Findings

Impurity properties remain isotropic without magnetic field.

Strong field-direction dependence of impurity spin polarization observed.

SOC can be measured via tunneling spectroscopy to determine Rashba and Dresselhaus ratios.

Abstract

Using the numerical renormalization group (NRG) method we study a magnetic impurity coupled to a quantum wire with Rashba and Dresselhaus spin-orbit coupling (SOC) in an external magnetic field. We consider the low-filling regime with the Fermi energy close to the bottom of the band and report the results for local static and dynamic properties in the Kondo regime. In the absence of the field, local impurity properties remain isotropic in spin space despite the SOC-induced magnetic anisotropy of the conduction band. In the presence of the field, clear fingerprints of anisotropy are revealed through the strong field-direction dependence of the impurity spin polarization and spectra, in particular of the Kondo peak height. The detailed behavior depends on the relative magnitudes of the impurity and band $g$-factors. For the case of impurity $g$-factor somewhat lower than the band $g$-factor, the maximal Kondo peak suppression is found for field oriented along the effective SOC field axis, while for a field perpendicular to this direction we observe a compensation effect (``revival of the Kondo peak''): the SOC counteracts the Kondo peak splitting effects of the local Zeeman field. We demonstrate that the SOC-induced anisotropy, measurable by tunneling spectroscopy techniques, can help to determine the ratio of Rashba and Dresselhaus SOC strengths in the wire.