Nonlinear Transport through NS Junctions due to Imperfect Andreev Reflection

TL;DR

This paper explores how nonlinear effects like current saturation, negative differential resistance, bistability, and hysteresis arise in NS junctions with few conducting channels due to imperfect Andreev reflection, especially as the Fermi energy drops below the gap.

Contribution

It introduces a detailed analysis of nonlinear transport phenomena in NS junctions with few channels, highlighting the impact of reduced Fermi energy on conduction behavior.

Findings

Observation of current saturation at low Fermi energies

Identification of N-shaped negative differential resistance

Detection of bistability and hysteresis in I-V characteristics

Abstract

We investigate a normal metal -- superconductor (point) contact in the limit where the number of conducting channels in the metallic wire is reduced to few channels. As the effective Fermi energy drops below the gap energy, a conducting band with a width twice the Fermi energy is formed. Depending on the mode of operation, the conduction band can be further squeezed, leading to various non-linear effects in the current-voltage characteristics such as current saturation, a N-shaped negative differential resistance, bistability, and hysteresis.