Spatially inhomogeneous superconductivity in UTe2

The newly discovered superconductor UTe2 is a strong contender for a topological spin-triplet state wherein a multicomponent order parameter arises from two nearly degenerate superconducting states. A key issue is
whether both of these states intrinsically exist at ambient pressure. Through thermal expansion and calorimetry, we show that UTe2 at ambient conditions exhibits two detectable transitions only in some samples, and the
size of the thermal expansion jump at each transition varies when the measurement is performed in different regions of the sample. This result indicates that the two transitions arise from two spatially separated regions
that are inhomogeneously mixed throughout the volume of the sample, each with a discrete superconducting transition temperature (Tc). Notably, samples with higher Tc only show a single transition at ambient pressure. Above 0.3 GPa, however, two transitions are invariably observed in ac calorimetry. Our results not only point to a nearly vertical line (constant pressure) in the pressure-temperature phase diagram but also provide a consistent scenario for the sample dependence of UTe2.