Ground-state properties of a large Coulomb-blockaded quantum dot

TL;DR

This paper investigates the ground-state properties of large Coulomb-blockaded quantum dots using renormalization-group techniques, revealing non-analytic behaviors and phase transitions influenced by electron interactions, tunneling, and spin symmetry.

Contribution

It extends previous results by analyzing the effects of interactions and spin symmetry on capacitance singularities and Coulomb blockade stability in quantum dots.

Findings

Capacitance exhibits logarithmic singularities for non-interacting electrons.

Logarithmic singularities persist with SU(2) spin symmetry and certain interactions.

Coulomb blockade undergoes a Kosterlitz-Thouless transition as tunneling increases.

Abstract

Using renormalization-group techniques we analyze equilibrium properties of a large gated quantum dot coupled via a long and narrow channel to a reservoir of electrons. Treating the electrons in the channel as one-dimensional and interacting, we demonstrate that for nearly-open dot and not very strong spin fluctuations the ground-state properties as a function of the gate voltage are non-analytic at the points of half-integer average dot population. Specifically, the exact result of K. A. Matveev, Phys. Rev. B 51, 1743 (1995), that the dot capacitance shows periodic logarithmic singularities is rederived as a special case corresponding to non-interacting electrons. We demonstrate that this conclusion also holds in the presence of SU(2) spin symmetry, and argue that logarithmic singularities persist as long as the Coulomb blockade is destroyed which will be the case for sufficiently large tunneling and not very strong interparticle repulsions. We show that interparticle repulsions aid the Coulomb blockade to survive disordering effect of zero-point motion provided the tunneling is sufficiently weak. Upon increase of tunneling, the Coulomb blockade disappears through a Kosterlitz-Thouless phase transition characterized by a dot population jump whose magnitude is only determined by interparticle repulsions in the channel. Similar conclusions are applicable to systems without SU(2) spin symmetry except that the logarithmic singularity of the capacitance is replaced by a power-law non-analyticity whose exponent characterizes the degree of spin fluctuations.