Low-temperature electron dephasing rates indicate magnetic disorder in superconducting TiN films

TL;DR

This study reveals that magnetic disorder near the surface of TiN films causes low-temperature electron dephasing, impacting superconducting properties and device performance.

Contribution

It provides evidence that surface magnetic disorder significantly influences electron dephasing in TiN films, a novel insight into their superconducting behavior.

Findings

Electron dephasing occurs on picosecond timescale and is temperature-independent.

Thinner films show increased dephasing rates, indicating surface magnetic disorder.

Magnetic disorder may contribute to RF dissipation in TiN-based superconducting devices.

Abstract

We investigate electron transport and phase-breaking processes in thin titanium nitride (TiN) films of epitaxial quality. Previous studies show that a minute surface magnetic disorder significantly reduces the critical temperature ($T_\mathrm{c}$) and broadens the superconducting transition as the film thickness and device size decrease. We measure electron dephasing rates via magnetoresistance from $T_\mathrm{c}$ to $\sim 4T_\mathrm{c}$ in various-thickness TiN films. Electron dephasing occurs on the picosecond timescale and is nearly independent of temperature, differing from the expected inelastic scattering due to the electron-phonon and electron-electron interactions near $T_\mathrm{c}$, which occur over a nanosecond timescale. We propose spin-flip scattering as a possible additional phase-breaking mechanism. The significant increase in the dephasing rate for the thinnest film indicates that magnetic disorder resides near the surface of naturally oxidized films. Our research suggests that magnetic disorder may be a significant contributor to RF dissipation in superconducting devices based on TiN.