Superfluid Density and Possible Time Reversal Symmetry Breaking in Candidate Spin-Triplet Superconductor Li0.9Mo6O17

Quasi-one-dimensional purple bronze Li0.9Mo6O17 (LMO) is a leading candidate for the realisation of a Tomonaga-Luttinger liquid (TLL) ground state in addition to exhibiting emergent symmetry at low temperature [1,2]. Superconductivity emerges out of this non-Fermi liquid normal state at Tc ≈ 2.3 K, with the upper critical field along the conductive axis, Hc2 ≈ 15 T, exceeding the Pauli paramagnetic limit, indicative of an unconventional spin-triplet pairing state [3]. Possible signatures of re-entrant superconductivity were also reported at 45 T [4]. Until now, however, no further studies of the symmetry and structure of the superconducting order parameter have been conducted, and the origin of the pairing in LMO has remained elusive.

We seek to answer outstanding questions surrounding the symmetry and structure of the order parameter in LMO with this muSR study. Firstly we will utilise zero-field muSR measurements to detect the formation of spontaneous magnetic fields within the sample that would indicate time reversal symmetry breaking. Secondly we will utilise transvers-field muSR measurements to determine the temperature dependence of the magnetic penetration depth in order to elucidate information on the structure of the energy gap.

[1] N. Wakeham et al., Nat Commun. 2, 396 (2011)
[2] P. Chudzinski et al., Science 382, 792 (2023)
[3] J.-F. Mercure et al., Phys. Rev. Lett. 108, 187003 (2012)
[4] X. Xu et al., Phys. Rev. Lett. 102, 206602 (2009)