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

TL;DR

This study investigates how uniaxial stress affects the superconducting and transport properties of UTe$_2$, revealing anisotropic effects on critical temperature and suggesting a single-component order parameter.

Contribution

It provides new experimental data on the effects of uniaxial stress along different crystallographic directions on UTe$_2$'s superconductivity and transport properties.

Findings

Critical temperature decreases with stress along [100] and [110]

Critical temperature increases with stress along [001]

In-plane shear stress does not split the superconducting transition

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 $\sigma$ 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.