e-h Coherence and Charging Effects in Ultrasmall Metallic Grains

TL;DR

This paper models electron tunneling between ultrasmall metallic grains, revealing a quantum phase transition from Coulomb blockade to a coherent state with potential relevance to granular materials and quantum dots.

Contribution

It introduces a model showing a quantum phase transition with non-equilibrium effects and electron-hole coherence in ultrasmall metallic grains.

Findings

Identification of a quantum phase transition between Coulomb blockade and coherent states.

Critical state exhibits temperature-independent resistance of order h/e^2.

Similarities drawn between the quantum transition and metal-insulator transition in granular wires.

Abstract

We consider a model for electron tunneling between a pair of ultrasmall metallic grains. Under appropriate circumstances, non-equilibrium final state effects can strongly enhance tunneling and produce electron-hole coherence between the grains. The model displays a quantum phase transition between a Coulomb blockaded state to a coherent state exhibiting subohmic tunneling conductance. The critical state of the junction exhibits a temperature independent resistance of order $h/e^2$. Finally we discuss the possible relevance to granular materials and quantum dots. In particular, similarities between the quantum transition in our model and the metal-insulator transition in granular wires observed by Herzog et al. are described in detail.