Thermodynamic and electrical transport properties of UTe${}_2$ under uniaxial stress

Abstract

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 $\ddot{I}ƒ$ applied along different crystallographic directions. We find that the critical temperature $T_{\mathrm{c}}$ of the single observed bulk superconducting transition decreases with $\ddot{I}ƒ$ along $[100]$ and $[110]$ but increases with $\ddot{I}ƒ$ along $[001]$. Aside from its effect on $T_{\mathrm{c}}$, we notice that $c$-axis stress leads to a significant piezoresistivity, which we associate with the shift of the zero-pressure resistivity peak at $T^{\star }\approx 15\mathrm{K}$ to lower temperatures under stress. Finally, we show that an in-plane shear stress $\ddot{I}{ƒ}_{xy}$ does not induce any observable splitting of the superconducting transition over a stress range of $\ddot{I}{ƒ}_{xy}\approx 0.17\mathrm{GPa}$. This result suggests that the superconducting order parameter of UTe${}_2$ may be single-component at ambient pressure.