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 applied along different crystallographic directions. We find that the critical temperature T_c of the single observed bulk superconducting transition decreases with stress applied along [100] and [110] but increases with stress along [001]. Aside from its effect on T_c, c-axis stress leads to a significant piezoresistivity. Importantly, an in-plane shear stress σ_xy does not induce any observable splitting of the superconducting transition over a stress range of σ_xy ≈ 0.17 GPa. This result suggests that the superconducting order parameter of UTe₂ may be single component at ambient pressure.