Kondo effect in carbon nanotube quantum dots with spin-orbit coupling

TL;DR

This paper explores how spin-orbit coupling affects the Kondo effect in carbon nanotube quantum dots, revealing symmetry breaking, resonance splitting, and a purely orbital Kondo effect in certain regimes.

Contribution

It provides a detailed analysis of the influence of spin-orbit coupling on the Kondo effect, including resonance splitting and the identification of microscopic cotunneling processes.

Findings

Spin-orbit coupling lifts degeneracy and breaks SU(4) symmetry.

Kondo resonance splits and forms multipeak structures under magnetic field.

A purely orbital Kondo effect occurs in the two-electron regime.

Abstract

Motivated by recent experimental observation of spin-orbit coupling in carbon nanotube quantum dots [F. Kuemmeth \textsl{et al.}, Nature (London) {\bf 452}, 448 (2008)], we investigate in detail its influence on the Kondo effect. The spin-orbit coupling intrinsically lifts out the fourfold degeneracy of a single electron in the dot, thereby breaking the SU(4) symmetry and splitting the Kondo resonance even at zero magnetic field. When the field is applied, the Kondo resonance further splits and exhibits fine multipeak structures resulting from the interplay of spin-orbit coupling and Zeeman effect. A microscopic cotunneling process for each peak can be uniquely identified. Finally, a purely orbital Kondo effect in the two-electron regime is also obtained.