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

TL;DR

This paper investigates the SU(4) Kondo effect in a triangular triple quantum dot system, revealing how a crossover to SU(2) symmetry induces emergent electric polarization and sign reversal, providing insights into orbital dynamics.

Contribution

It demonstrates the SU(4) to SU(2) crossover in a TTQD system and links this transition to emergent electric polarization, using numerical renormalization group analysis.

Findings

Emergent electric polarization linked to SU(4) to SU(2) crossover.

Sign reversal of polarization via fine-tuning Kondo coupling.

Identification of orbital dynamics in the Kondo effect.

Abstract

We study an orbitally degenerate Kondo effect in a triangular triple quantum dot (TTQD), where the three dots are connected vertically with a single metallic lead through electron tunneling. Both spin and orbital degrees of freedom play an important role in the SU(4) Kondo effect. This is demonstrated by an equilateral TTQD Kondo system at half-filling, by Wilson's numerical renormalization group method. We show how an emergent electric polarization of the TTQD is associated with a crossover from SU(4) to SU(2) symmetry in the low-temperature state. A marked sign reversal of the electric polarization is generated by the fine-tuning of Kondo coupling with degenerate orbitals, which can be utilized to reveal orbital dynamics in the SU(4) Kondo effect.