Competing superconducting states in UTe2 revealed by thermal expansion

Newly-discovered superconductor UTe$_2$ is a strong contender for a topological spin-triplet state, which has been argued to stem from a multi-component order parameter arising from two nearly-degenerate superconducting states. A key issue is whether both of these states intrinsically exist under ambient-pressure conditions. Through thermal expansion and calorimetry, we show that UTe$_2$ invariably exhibits two transitions as a function of pressure, independent of growth conditions. Further, the transitions have opposite pressure dependence, as determined by the Ehrenfest relation, in agreement with prior pressure studies. Nonetheless, variations in synthesis conditions affect the balance between these two competing superconducting states.