Kondo effects in small bandgap carbon nanotube quantum dots

TL;DR

This paper investigates the complex Kondo effects in small bandgap carbon nanotube quantum dots under magnetic fields, revealing various symmetry restorations and the potential for electron-hole Kondo effects in specific magnetic orientations.

Contribution

It introduces a detailed analysis of magnetic field-induced symmetry changes and Kondo effects in carbon nanotube quantum dots using a finite-U mean field slave boson approach.

Findings

Multiple Kondo symmetries (SU(2), SU(3), SU(4)) are identified under different magnetic field orientations.

Electron-hole Kondo effects are predicted to occur in slanting magnetic fields.

A crossover from SU(2)/SU(3) to SU(4) symmetry is observed as the magnetic field orientation changes.

Abstract

We study magnetoconductance of the small bandgap carbon nanotube quantum dots in the presence of spin-orbit coupling in the strong correlations regime. The finite-U mean field slave boson approach is used to study many-body effects. Different degeneracies are restored in magnetic field and Kondo effects of different symmetries arise including SU(3) effects of different types. Full spin-orbital degeneracy might be recovered for zero field and correspondingly SU(4) Kondo effect sets in. We point out on the possibility of the occurrence of electron-hole Kondo effects in slanting magnetic fields, which we predict will occur in the available magnetic fields for orientation of fields close to perpendicular. When the field approaches transverse orientation a crossover from SU(2) or SU(3) symmetry into SU(4) is observed.