SU(4) and SU(2) Kondo Effects in Carbon Nanotube Quantum Dots

摘要

We study the SU(4) Kondo effect in carbon nanotube quantum dots, where doublydegenerate orbitals form 4-electron ``shells''. The SU(4) Kondo behavior isinvestigated for one, two and three electrons in the topmost shell. While theKondo state of two electrons is quenched by magnetic field, in case of an oddnumber of electrons two types of SU(2) Kondo effect may survive. Namely, thespin SU(2) state is realized in the magnetic field parallel to the nanotube(inducing primarily orbital splitting). Application of the perpendicular field(inducing Zeeman splitting) results in the orbital SU(2) Kondo effect.