Thermodynamic and electrical transport properties of UTe\(_2\) under uniaxial stress

Despite intense experimental efforts, the nature of the unconventional superconducting order parameter of UTe\(_2\) remains elusive. This puzzle stems from different reported numbers of superconducting transitions at ambient pressure, as well as a complex pressure-temperature phase diagram. To bring new insights into the superconducting properties of UTe\(_2\), we measured the heat capacity and electrical resistivity of single crystals under compressive uniaxial stress \(\sigma\) applied along different crystallographic directions. We find that the critical temperature \(T_{\rm c}\) of the single observed bulk superconducting transition decreases with \(\sigma\) along \([100]\) and \([110]\) but increases with \(\sigma\) along \([001]\). Aside from its effect on \(T_{\rm c}\), we notice that \(c\)-axis stress leads to a significant piezoresistivity, which we associate with the shift of the zero-pressure resistivity peak at \(T^\star \approx 15\, \rm K\) to lower temperatures under stress. Finally, we show that an in-plane shear stress \(\sigma_{xy}\) does not induce any observable splitting of the superconducting transition over a stress range of \(\sigma_{xy}\approx 0.17 \, \rm GPa\). This result suggests that the superconducting order parameter of UTe\(_2\) may be single-component at ambient pressure.