The pairing symmetry in quasi-one-dimensional superconductor Rb2Mo3As3

TL;DR

This study investigates the superconducting pairing symmetry in Rb2Mo3As3 using muon spin rotation, finding evidence for s-wave pairing but cannot exclude nodal p- or d-wave symmetries due to similar fits.

Contribution

First muon spin rotation study of Rb2Mo3As3 revealing its pairing symmetry and superconducting gap characteristics among quasi-one-dimensional superconductors.

Findings

Best fit with s-wave model but with small gap ratio

Nodal p- or d-wave scenarios are also plausible

Superconducting transition temperature is 10.4 K

Abstract

Quasi-one-dimensional electron systems display intrinsic instability towards long-range ordered phases at sufficiently low temperatures. The superconducting orders are of particular interest as they can possess either singlet or triplet pairing symmetry and frequently compete with magnetism. Here we report on muon spin rotation and relaxation ($\mathrm{\mu}$SR) study of Rb$_2$Mo$_3$As$_3$ characterised by one of the highest critical temperatures $T_{\rm c}=10.4\ \mathrm{K}$ among quasi-one-dimensional superconductors. The transverse-field $\mathrm{\mu}$SR signal shows enhanced damping below $T_{\rm c}$ due to the formation of vortex lattice. Comparison of vortex lattice broadening against single gap $s-$, $p-$ and $d-$wave models shows the best agreement for the $s-$wave scenario but with the anomalously small superconducting gap, $\Delta_0$, to $T_{\rm c}$ ratio of $2\Delta_0/k_{\rm B}T_{\rm c}=2.74(1)$. The alternative nodal $p-$wave or $d-$wave scenarios with marginally worse goodness of fit would yield more realistic $2\Delta_0/k_{\rm B}T_{\rm c}=3.50(2)$ and $2\Delta_0/k_{\rm B}T_{\rm c}=4.08(1)$, respectively, and thus they cannot be ruled out when accounting for the superconducting state in Rb$_2$Mo$_3$As$_3$.