Thermodynamic and electrical transport properties of UTe2 under uniaxial stress

Despite intense experimental efforts, the nature of the unconventional superconducting order parameter of UTe2 remains elusive. This puzzle stems from reports of either a single or a double superconducting transition at ambient pressure as well as a complex pressure-temperature phase diagram. To address this issue, we measured the heat capacity and electrical resistivity of UTe2 under compressive uniaxial stress σ applied along different crystallographic directions. We find that the critical temperature Tc of the single observed bulk superconducting transition decreases with σ along [100] and [110] but increases with σ along [001]. Aside from its effect on Tc, c-axis stress leads to a significant piezoresistivity. Importantly, an in-plane shear stress σxy does not induce any observable splitting of the superconducting transition over a stress range of σxy≈0.17GPa. This result suggests that the superconducting order parameter of UTe2 may be single component at ambient pressure.