New Numerical Results Indicate a Half-Filling SU(4) Kondo State in Carbon Nanotubes

TL;DR

This paper presents numerical evidence that the Kondo effect observed in carbon nanotube quantum dots at half-filling exhibits SU(4) symmetry, revealing complex many-body physics and challenging previous interpretations of experimental data.

Contribution

The study demonstrates that the Kondo conductance at half-filling in carbon nanotubes is consistent with an SU(4) Kondo state, providing new insights into the symmetry and physical behavior of these systems.

Findings

Half-filling SU(4) Kondo state identified in simulations

Reinterpretation of experimental conductance data as SU(4) Kondo effect

Rich physical phenomena including non-Fermi-liquid behavior associated with SU(4)

Abstract

Numerical calculations simulate transport experiments in carbon nanotube quantum dots (P. Jarillo-Herrero et al., Nature 434, 484 (2005)), where a strongly enhanced Kondo temperature T_K ~ 8K was associated with the SU(4) symmetry of the Hamiltonian at quarter-filling for an orbitally double-degenerate single-occupied electronic shell. Our results clearly suggest that the Kondo conductance measured for an adjacent shell with T_K ~ 16K, interpreted as a singlet-triplet Kondo effect, can be associated instead to an SU(4) Kondo effect at half-filling. Besides presenting spin-charge Kondo screening similar to the quarter-filling SU(4), the half-filling SU(4) has been recently associated to very rich physical behavior, including a non-Fermi-liquid state (M. R. Galpin et al., Phys. Rev. Lett. 94, 186406 (2005)).