Charge quantization in S–I–N Coulomb blockade structures

Abstract

We study the crossover between the Coulomb blockade and proximity-induced superconductivity in a small normal island connected by a tunnel junction to a superconducting lead. Unlike the N–I–N case, the steps of the Coulomb staircase remain sharp even if the conductance of the tunneling barrier exceeds e 2/ h. The crossover occurs only at a larger conductance, G *∼(e 2/ℏ) Δ/δ , where Δ and δ are the superconducting gap and average level spacing in the lead and island respectively.