Gate-tunable negative differential conductance in hybrid semiconductor-superconductor devices

TL;DR

This study demonstrates gate-tunable negative differential conductance in hybrid semiconductor-superconductor devices, revealing how it depends on voltage, magnetic field, and superconducting gap, advancing understanding of tunneling transport mechanisms.

Contribution

We introduce the BTK-supercurrent model to explain gate and magnetic field effects on NDC in hybrid devices, providing new insights into their transport properties.

Findings

NDC weakens and shifts with gate voltage and magnetic field.

NDC disappears when the superconducting gap closes.

The BTK-supercurrent model accurately explains observed behaviors.

Abstract

Negative differential conductance (NDC) manifests as a significant characteristic of various underlying physics and transport processes in hybrid superconducting devices. In this work, we report the observation of gate-tunable NDC outside the superconducting energy gap on two types of hybrid semiconductor-superconductor devices, i.e., normal metal-superconducting nanowire-normal metal and normal metal-superconducting nanowire-superconductor devices. Specifically, we study the dependence of the NDCs on back-gate voltage and magnetic field. When the back-gate voltage decreases, these NDCs weaken and evolve into positive differential conductance dips; and meanwhile they move away from the superconducting gap towards high bias voltage, and disappear eventually. In addition, with the increase of magnetic field, the NDCs/dips follow the evolution of the superconducting gap, and disappear when the gap closes. We interpret these observations and reach a good agreement by combining the Blonder-Tinkham-Klapwijk (BTK) model and the critical supercurrent effect in the nanowire, which we call the BTK-supercurrent model. Our results provide an in-depth understanding of the tunneling transport in hybrid semiconductor-superconductor devices.