Nonequilibrium and Parity Effects in the Tunneling Conductance of Ultrasmall Superconducting Grains

TL;DR

This paper explains unusual tunneling conductance peaks in ultrasmall superconducting grains by nonequilibrium gapless excitations caused by inelastic cotunneling, revealing new insights into quantum effects in nanoscale superconductors.

Contribution

It introduces a novel explanation for the conductance peak structure based on nonequilibrium excitations in ultrasmall grains.

Findings

Unusual conductance peak structure observed in experiments.

Nonequilibrium gapless excitations account for the behavior.

Inelastic cotunneling generates these excitations.

Abstract

Recent experiment on the tunneling spectra of ultrasmall superconducting grains revealed an unusual structure of the lowest differential conductance peak for grains in the odd charging states. We explain this behavior by nonequilibrium ``gapless'' excitations associated with different energy levels occupied by the unpaired electron. These excitations are generated by inelastic cotunneling.