The superconducting energy gap of Ba1−xKxBiO3 has been measured by tunneling. Despite the fact that the sample was macroscopically single phase with very sharp superconducting transition Tc at 32~K, some of the measured tunnel junctions made by point contacts between silver tip and single crystal of Ba1−xKxBiO3 had lower transition at 20~K. Local variation of the potassium concentration as well as oxygen deficiency in Ba1−xKxBiO3 at the place where the point contact is made can account for the change of Tc. 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 Tc. The reduced gap amounts to 2Δ/kTc=4÷4.3 indicating a medium coupling strength. Temperature dependence of the energy gap follows the BCS prediction.
@article{arxiv.1704.00285,
title = {Superconducting energy gap in $\rm Ba_{1-x}K_xBiO_3$: Temperature dependence},
author = {F. Szabo and P. Samuely and N. L. Bobrov and J. Marcus and C. Escribe-Filippini and M. Affronte},
journal= {arXiv preprint arXiv:1704.00285},
year = {2017}
}