# Superconducting energy gap in $\rm Ba_{1-x}K_xBiO_3$: Temperature dependence

## TL;DR

This study measures the superconducting energy gap in Ba_{1-x}K_xBiO_3 using tunneling, revealing BCS-like behavior with a medium coupling strength and temperature dependence consistent with theoretical predictions.

## Contribution

It provides experimental data on the energy gap and its temperature dependence in Ba_{1-x}K_xBiO_3, highlighting local variations affecting the transition temperature.

## Key findings

- Energy gap scales with T_c
- Reduced gap ratio of 4-4.3 indicating medium coupling
- Temperature dependence follows BCS theory

## Abstract

The superconducting energy gap of $\rm Ba_{1-x}K_xBiO_3$ has been measured by tunneling. Despite the fact that the sample was macroscopically single phase with very sharp superconducting transition $T_c$ at 32~$K$, some of the measured tunnel junctions made by point contacts between silver tip and single crystal of $\rm Ba_{1-x}K_xBiO_3$ had lower transition at 20~$K$. Local variation of the potassium concentration as well as oxygen deficiency in $\rm Ba_{1-x}K_xBiO_3$ at the place where the point contact is made can account for the change of $T_c$. The conductance curves of the tunnel junctions reveal the BCS behavior with a small broadening of the superconducting-gap structure. A value of the energy gap scales with $T_c$. The reduced gap amounts to $2\Delta/kT_c = 4\div 4.3$ indicating a medium coupling strength. Temperature dependence of the energy gap follows the BCS prediction.