Interplay between Kondo physics and spin-orbit coupling in carbon nanotube quantum dots

TL;DR

This paper explores how spin-orbit coupling affects Kondo phenomena in carbon nanotube quantum dots, revealing the suppression and emergence of various SU(2) Kondo effects under different conditions, with results matching experimental data.

Contribution

It demonstrates the impact of spin-orbit coupling on Kondo effects and explains experimental observations beyond the standard SU(4) Anderson model.

Findings

Large spin-orbit coupling destroys SU(4) Kondo effects at zero field.

Finite magnetic fields induce additional SU(2) Kondo effects.

Calculated conductance matches experimental measurements.

Abstract

We investigate the influence of spin-orbit coupling on the Kondo effects in carbon nanotube quantum dots, using the numerical renormalization group technique. A sufficiently large spin-orbit coupling is shown to destroy the SU(4) Kondo effects at zero magnetic field, leaving only two SU(2) Kondo effects in the one- and three-electron Coulomb blockade valleys. On applying a finite magnetic field, two additional, spin-orbit induced SU(2) Kondo effects arise in the three- and two-electron valleys. Using physically realistic model parameters, we calculate the differential conductance over a range of gate voltages, temperatures and fields. The results agree well with measurements from two different experimental devices in the literature, and explain a number of observations that are not described within the standard framework of the SU(4) Anderson impurity model.