Mapping the superconducting phase of UTe₂ under uniaxial stress

The recently discovered uranium-based unconventional superconductor UTe₂ has attracted attention as a promising candidate for spin-triplet pairing and topological superconductivity. Among its numerous peculiarities, UTe₂ hosts different superconducting phases as a function of applied hydrostatic pressure and magnetic fields. For hydrostatic pressures exceeding 0.3 GPa, UTe₂ exhibits two superconducting transitions that have opposite pressure dependence. At zero field and ambient pressure, UTe₂ crystals with an optimal superconducting transition temperature, T_c = 2 K, host a single thermodynamic superconducting transition. Some reports, however, argue that a multi-component order parameter exists even at ambient pressure. Due to its orthorhombic structure symmetry, any multi-component order parameter should lead to two non-degenerate superconducting transitions in UTe₂. The reason multiple transitions are not observed below P = 0.3 GPa in the highest quality crystals remains unknown, as does the sudden emergence of two transitions at P = 0.3 GPa. Here, we investigate the uniaxial stress dependence of the low temperature specific heat and electrical resistivity of UTe₂ along different crystallographic directions to better understand the pressure-temperature phase diagram of UTe₂.