Suppression of low-energy Andreev states by a supercurrent in YBa_2Cu_3O_7-delta

TL;DR

This study investigates how a supercurrent affects low-energy Andreev states in YBa_2Cu_3O_7-delta, revealing suppression of these states without changing the superconducting gap, indicating phase fluctuations influence local coherence.

Contribution

It demonstrates that a supercurrent can suppress Andreev states via phase fluctuations in a high-Tc superconductor, providing new insights into supercurrent effects on local electronic states.

Findings

Supercurrent suppresses low-energy Andreev states

Superconducting gap remains unchanged under supercurrent

Phase fluctuations may weaken local phase coherence

Abstract

We report a coherence-length scale phenomenon related to how the high-Tc order parameter (OP) evolves under a directly-applied supercurrent. Scanning tunneling spectroscopy was performed on current-carrying YBa_2Cu_3O_7-delta thin-film strips at 4.2K. At current levels well below the theoretical depairing limit, the low-energy Andreev states are suppressed by the supercurrent, while the gap-like structures remain unchanged. We rule out the likelihood of various extrinsic effects, and propose instead a model based on phase fluctuations in the d-wave BTK formalism to explain the suppression. Our results suggest that a supercurrent could weaken the local phase coherence while preserving the pairing amplitude. Other possible scenarios which may cause the observed phenomenon are also discussed.