Chiral singlet superconductivity in the weakly correlated metal LaPt3P

TL;DR

This paper reports that LaPt3P is a chiral d-wave singlet superconductor with broken time-reversal symmetry and line nodes, confirmed through muSR measurements, symmetry analysis, and theoretical calculations.

Contribution

It provides the first evidence of chiral singlet superconductivity in LaPt3P, combining experimental and theoretical approaches.

Findings

Spontaneous magnetic fields indicating broken TRS

Linear superfluid density at low temperatures suggesting line nodes

Identification of chiral d-wave singlet pairing in LaPt3P

Abstract

Topological superconductors (SCs) are novel phases of matter with nontrivial bulk topology. They host at their boundaries and vortex cores zero-energy Majorana bound states, potentially useful in fault-tolerant quantum computation. Chiral SCs are particular examples of topological SCs with finite angular momentum Cooper pairs circulating around a unique chiral axis, thus spontaneously breaking time-reversal symmetry (TRS). They are rather scarce and usually feature triplet pairing: best studied examples in bulk materials are UPt3 and Sr2RuO4 proposed to be f-wave and p-wave SCs respectively, although many open questions still remain. Chiral triplet SCs are, however, topologically fragile with the gapless Majorana modes weakly protected against symmetry preserving perturbations in contrast to chiral singlet SCs. Using muon spin relaxation (muSR) measurements, here we report that the weakly correlated pnictide compound LaPt3P has the two key features of a chiral SC: spontaneous magnetic fields inside the superconducting state indicating broken TRS and low temperature linear behaviour in the superfluid density indicating line nodes in the order parameter. Using symmetry analysis, first principles band structure calculation and mean-field theory, we unambiguously establish that the superconducting ground state of LaPt3P is chiral d-wave singlet.