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/e2. 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.
@article{arxiv.cond-mat/9707014,
title = {e-h Coherence and Charging Effects in Ultrasmall Metallic Grains},
author = {S. Drewes and S. R. Renn and F. Guinea},
journal= {arXiv preprint arXiv:cond-mat/9707014},
year = {2009}
}