# Tunneling measurements of the electron-phonon interaction in $\rm Ba_{1-x}K_xBiO_3$

## TL;DR

This study uses tunneling measurements to analyze the electron-phonon interaction in Ba_{1-x}K_xBiO_3, revealing the significance of oxygen optical modes in its superconductivity through spectral function analysis.

## Contribution

It provides detailed tunneling data and spectral analysis of electron-phonon coupling in Ba_{1-x}K_xBiO_3, highlighting the role of oxygen optical modes in its superconducting mechanism.

## Key findings

- Reproducible peaks in d^2V/dI^2 stable up to transition temperature
- Spectral function α^2F indicates strong electron-phonon coupling
- Oxygen optical modes are significant in superconductivity

## Abstract

The conductance curves of point-contact tunnel junctions between Ag and $\rm Ba_{1-x}K_xBiO_3$ ($x\simeq 0.4$) reveal a BCS behavior with low leakage current at zero voltage and some broadening of the superconducting-gap structure. In the energy range above the superconducting energy gap, the structure in the voltage dependence of the second derivative $d^2V/dI^2$ of the voltage with respect to the current of the tunnel junction has been investigated in detail in magnetic fields up to $10\ T$. While part of this structure is rapidly changing in a magnetic field, three reproducible peaks in $d^2V/dI^2(V)$ remain stable up to the transition temperature from the superconducting to the normal state with only additional broadening in the applied magnetic field. An analysis of this structure in terms of strong-coupling effects yields the spectral function $\alpha^2F$ for the electron-phonon interaction. The obtained spectral weight in the energy region 20-70~$meV$ points to the importance of the oxygen optical modes in the electron-phonon coupling for the superconductivity of $\rm Ba_{1-x}K_xBiO_3$.