Quantum Phase Transition in Capacitively Coupled Double Quantum Dots

Abstract

We investigate two equivalent, capacitively coupled semiconducting quantum dots, each coupled to its own lead, in a regime where there are two electrons on the double dot. With increasing interdot coupling, a rich range of behavior is uncovered: first a crossover from spin- to charge-Kondo physics, via an intermediate SU(4) state with entangled spin and charge degrees of freedom, followed by a quantum phase transition of Kosterlitz-Thouless type to a non-Fermi-liquid "charge-ordered" phase with finite residual entropy and anomalous transport properties. Physical arguments and numerical renormalization group methods are employed to obtain a detailed understanding of the problem.

Quantum phase transition and underscreened Kondo effect in electron transport through parallel double quantum dots

“…For DQDs with large capacitive coupling, the simultaneous appearance of the Kondo effect in the spin and charge sectors results in an SU(4) Fermi liquid ground state [8]. By increasing interdot capacitive coupling, a quantum phase transition of Kosterlitz-Thouless type to a non-Fermi-liquid state with anomalous transport properties is predicted [9]. Martins et al argued that ferromagnetic state cannot be realized in two single-level QDs connected in serial, but they predicts that FM state can be developed in two double-level QDs [10].…”

Spin-orbital Kondo effect in a parallel double quantum dot

“…The two-orbital Kondo effect is a many-body phenomenon that has been investigated for carbon-nanotube quantum dots (QDs), [1][2][3][4] vertical QDs, 5 and parallel double quantum dots (DQDs), [6][7][8][9][10][11][12][13][14][15][16][17] where a localized state in the QDs has spin and orbital (pseudospin) internal degrees of freedom. Since the orbital degree of freedom plays the role of pseudospin in addition to spin, the Kondo correlation involves both spin and pseudospin flip events, and their strong mixing leads to spin-orbital Kondo properties that are in marked contrast to an ordinary SU(2) spin-Kondo effect, in which only spin flip events are involved.…”

Analysis of low-energy response and possible emergent SU(4) Kondo state in a double quantum dot

“…The Anderson model with U 12 = U can be mapped into a SU(4) Kondo model also in the case with particle-hole symmetry with n d,1 = n d,2 = 1. 31 In this case the operators in the model correspond to a 6-dimensional representation of SU(4) in contrast to the mapping for the spin/pseudospin degenerate model with n d,1 = n d,2 = 0.5 where the operators correspond to the fundamental (4-dimensional) representation of SU (4).…”

“…[1][2][3][4][5][6][7][8][9] As a consequence of this confinement, the on-site and inter-site interactions between the electrons on the dots are strong and their coupling to their environmental electron baths relatively weak. Such systems can be used to probe the effects of strong local electron correlation, such as the Kondo effect, in great detail.…”