Coulomb blockade and Quantum Critical Points in Quantum Dots

TL;DR

This paper investigates a quantum dot system coupled to a lead and a quantum box, revealing a line of unstable non-Fermi-liquid fixed points that control the crossover between different conductance regimes, with implications for quantum criticality.

Contribution

It identifies and characterizes a line of quantum-critical fixed points in a coupled quantum dot system, extending understanding of non-Fermi-liquid behavior and quantum phase transitions.

Findings

Discovery of a line of unstable non-Fermi-liquid fixed points.

Fixed points possess finite residual entropy.

Crossover between Fermi-liquid regimes with distinct conductance values.

Abstract

An ultrasmall quantum dot coupled to a lead and to a quantum box (a large quantum dot) is investigated. Tuning the tunneling amplitudes to the lead and box, we find a line of unstable non-Fermi-liquid fixed points as function of the gate potentials of the quantum dots, extending to arbitrary charging energies on the small and large quantum dots. These quantum-critical fixed points possess a finite residual entropy. They govern the cross over from one Fermi-liquid regime to another, characterized by distinct (high and low) conductance values.