Phase Diffusion in Single-Walled Carbon Nanotube Josephson Transistors

TL;DR

This paper studies phase diffusion effects in single-walled carbon nanotube Josephson transistors, revealing enhanced conductance, sub-harmonic gap structures, and gate-tunable switching currents consistent with classical phase diffusion models.

Contribution

It provides experimental evidence of phase diffusion phenomena in nanotube-based Josephson junctions and correlates observed behaviors with theoretical models.

Findings

Enhanced zero-bias conductance up to 10e^2/h

Pronounced sub-harmonic gap structures from multiple Andreev reflections

Gate-tunable switching current from 50 pA to 2.3 nA

Abstract

We investigate electronic transport in Josephson junctions formed by single-walled carbon nanotubes coupled to superconducting electrodes. We observe enhanced zero-bias conductance (up to 10e^2/h) and pronounced sub-harmonic gap structures in differential conductance, which arise from the multiple Andreev reflections at superconductor/nanotube interfaces. The voltage-current characteristics of these junctions display abrupt switching from the supercurrent branch to resistive branch, with a gate-tunable switching current ranging from 50 pA to 2.3 nA. The finite resistance observed on the supercurrent branch and the magnitude of the switching current are in good agreement with calculation based on the model of classical phase diffusion.