SU(2)-SU(4) Kondo Crossover and Emergent Electric Polarization in a Triangular Triple Quantum Dot

摘要

We study an orbitally degenerate Kondo effect in a triangular triple quantumdot (TTQD), where the three dots are connected vertically with a singlemetallic lead through electron tunneling. Both spin and orbital degrees offreedom play an important role in the SU(4) Kondo effect. This is demonstratedby an equilateral TTQD Kondo system at half-filling, by Wilson's numericalrenormalization group method. We show how an emergent electric polarization ofthe TTQD is associated with a crossover from SU(4) to SU(2) symmetry in thelow-temperature state. A marked sign reversal of the electric polarization isgenerated by the fine-tuning of Kondo coupling with degenerate orbitals, whichcan be utilized to reveal orbital dynamics in the SU(4) Kondo effect.