Pairing Correlation Effect on the Zero-Bias Tunneling Spectra of Ultrasmall Superconducting Grains

Abstract

We study the superconducting pairing correlation (SPC) effect on the resonant tunneling through an ultrasmall metallic grain with a gate electrode. The resonant conductance peaks appearing with an increase or decrease of the gate voltage are accompanied by the transition of the total electron number N on the grain, such as N ↔ N ± 1. We focus our attention on the tunneling resonance associated with an odd-N state. In the absence of the SPC effect, the structure of the zero-bias resonant conductance peak for N ↔ N - 1 is equivalent to that for N ↔ N + 1. It is shown that due to the interplay between the SPC effect and the nonuniform spacings of single-particle energy levels, we expect a notable difference between the two peak structures.