Quantum muon diffusion and the preservation of time-reversal symmetry in the superconducting state of type-I rhenium

TL;DR

This study shows that in type-I rhenium, unlike type-II, time-reversal symmetry remains intact in the superconducting state, with muon diffusion caused by quantum tunneling observed.

Contribution

It provides the first evidence that type-I rhenium preserves time-reversal symmetry in superconductivity, contrasting previous findings in type-II rhenium.

Findings

Time-reversal symmetry is preserved in type-I rhenium superconductivity.

Muon diffusion occurs due to quantum tunneling between interstitial sites.

Normal and superconducting states show typical metallic behavior.

Abstract

Elemental rhenium exhibiting type-II superconductivity has been previously reported to break time-reversal symmetry in the superconducting state. We have investigated an arc-melted sample of rhenium exhibiting type-I superconductivity. Low temperature zero-field muon-spin relaxation measurements indicate that time-reversal symmetry is preserved in the superconducting state. Muon diffusion is observed, which is due to quantum mechanical tunneling between interstitial sites. The normal state behavior is characterized by the conduction electrons screening the muons and thermal broadening, and is typical for a metal. Energy asymmetries between muon trapping sites and the superconducting energy gap also characterize the superconducting state behavior.