Surface symmetry breaking and disorder effects on superconductivity in perovskite BaBi3 epitaxial films

TL;DR

This study investigates how surface symmetry breaking and disorder influence superconductivity in BaBi3 epitaxial films, revealing anisotropic pairing and the role of disorder in quasiparticle excitations.

Contribution

It combines experimental STM data and first-principles calculations to elucidate the effects of symmetry breaking and disorder on superconductivity in BaBi3 films.

Findings

Broken rotational symmetry causes anisotropic superconductivity.

Disorder smears out electron pairing anisotropy in thin films.

A model of superconducting fluctuations explains tunneling spectra.

Abstract

The structural or electronic symmetry breaking of the host lattice is a recurrent phenomenon in many quantum materials, including superconductors. Yet, how these broken symmetry states affect the electronic pair wave function of superconductivity have been rarely elucidated. Here, using low-temperature scanning tunneling microscopy and first-principles calculations, we identify the broken rotational symmetry via stripe ordering on the (001) surface of perovskite BaBi3 films grown by molecular beam epitaxy, and show that it consequently leads to anisotropic superconductivity with twofold symmetry. In contrast, the structural disorder smears out the anisotropy of electron pairing and fills superconducting subgap density of states as the film thickness is reduced. A quasi-long range model of superconducting fluctuations is revealed to describe the tunneling conductance spectra of thin BaBi3 films well, and to exemplify how disorders contribute to the low-energy quasiparticle excitations in superconductors. Our findings help understand the effects of symmetry breaking states and disorders on superconductivity, particularly the existing tunneling conductance spectra there.