Scanning tunneling spectroscopy of a-axis YBa_2Cu_3O_7-\delta films:k-selectivity and the shape of the superconductor

TL;DR

This study uses scanning tunneling spectroscopy on YBa2Cu3O7−δ films to explore how tunneling probability depends on wave-vector, revealing insights into the superconductor's gap shape and surface effects at low temperature.

Contribution

It demonstrates the importance of wave-vector selectivity in tunneling spectra of YBa2Cu3O7−δ and discusses its origins, providing a detailed analysis of surface and nanofaceting effects.

Findings

Atomically smooth areas show U-shaped gaps fitting d-wave theory with k-selectivity.

Surface irregularities lead to V-shaped gaps and zero bias peaks.

Wave-vector dependence influences the interpretation of tunneling spectra.

Abstract

Tunneling spectroscopy of epitaxial (100) oriented \chem{YBa_2Cu_3O_{7-\delta}} films was performed using an STM at 4.2 K. On atomically smooth areas, tunneling spectra revealing clear U-shaped gaps with relatively low zero bias conductance were measured. These spectra can be well fitted to the tunneling theory into a d-wave superconductor only when introducing a strong dependence of the tunneling probability on the wave-vector \emph{\textbf{k}}. Possible origins for this \emph{\textbf{k}}-selectivity in STM measurements will be discussed. On other areas, V-shaped gaps as well as zero bias conductance peaks are observed, indicating relaxation of \emph{\textbf{k}}-selectivity and the effect of nanofaceting, respectively.