Critical Role of Disorder for Superconductivity in the Series of Epitaxial Ti(O,N) Films

TL;DR

This study reveals that disorder plays a crucial role in enhancing superconductivity in Ti(O,N) films, with nitrogen substitution increasing Tc and resistivity, challenging traditional theories and highlighting the importance of disorder in superconducting materials.

Contribution

It demonstrates how disorder influences superconductivity in Ti(O,N) films, combining experimental MBE growth and DFT calculations to reveal the weakening of electron-phonon coupling due to disorder.

Findings

Nitrogen substitution increases Tc and conductivity in TiO films.

Resistivity follows Mooij rule, indicating metallic glass behavior.

Disorder weakens electron-phonon coupling, affecting superconductivity.

Abstract

Realizing experimental control of superconductivity is of paramount importance to advancing both basic research and technological applications. Disorder, generally existing in most superconductors, intricately interacts with Cooper pairs and also impacts the performance of quantum devices. In this paper, we report the study of a series of Ti(O,N) crystalline films prepared via molecular beam epitaxy (MBE). We discover that substituting nitrogen (N) for oxygen (O) in TiO, namely TiO(N), considerably increases the normal-state conductivity and the superconducting transition temperature Tc. The Tc of TiO(N) falling between those of TiO (about 0.5 K) and TiN (about 6 K) is contrary to their comparable Tc predicted by the Migdal Eliasberg theory. It is found that their resistivity vs temperature obeys the Mooij rule, known as the characteristic of metallic glasses. Density functional theory (DFT) calculations demonstrate that strong disorder severely scatters the Bloch electron waves at nonzero momenta, which consequently weakens electron-phonon coupling in TiO(N).