Subharmonic gap structure in superconducting scanning tunneling microscope junctions

TL;DR

This study investigates the subharmonic gap structure and Josephson effect in superconducting STM junctions, revealing how phase fluctuations influence the Josephson dynamics and SGS features.

Contribution

It provides experimental evidence of SGS scaling with conductance and analyzes phase fluctuations' impact on Josephson oscillations in superconducting junctions.

Findings

SGS magnitude scales with the square of conductance

Josephson phase dynamics are strongly affected by thermal fluctuations

Sharp SGS onsets are not limited by phase fluctuations

Abstract

We observe a subharmonic gap sturucture (SGS) and the Josephson effect in superconducting scanning tunneling microscope junctions with resistances below 100 kOhm. The magnitude of the n=2 SGS is shown to scale with the square of the junction normal state conductance, in agreement with theory. We show by analyzing the Josephson effect in these junctions that the superconducting phase dynamics are strongly affected by thermal fluctuations. We estimate the linewidth of the Josephson oscillations due to phase fluctuations, a quantity that may be important in modern theories of the subgap structure. While phase fluctuations may smear the SGS current onsets, we conclude that the sharpness of these onsets in our data is not limited by fluctuations.