Tuning a magnetic energy scale with pressure in UTe$_2$

Abstract

A fragile ordered state can be easily tuned by various external parameters. When the ordered state is suppressed to zero temperature, a quantum phase transition occurs, which is often marked by the appearance of unconventional superconductivity. While the quantum critical point can be hidden, the influence of the quantum criticality extends to fairly high temperatures, manifesting the non-Fermi liquid behavior in the wide range of the $p$-$H$-$T$ phase space. Here, we report the tuning of a magnetic energy scale in the heavy-fermion superconductor UTe$_2$, previously identified as a peak in the $c$-axis electrical transport, with applied hydrostatic pressure and magnetic field along the $a$-axis as complementary (and opposing) tuning parameters. Upon increasing pressure, the characteristic $c$-axis peak moves to a lower temperature before vanishing near the critical pressure of about 15 kbar. The application of a magnetic field broadens the peak under all studied pressure values. The observed Fermi-liquid behavior at ambient pressure is violated near the critical pressure, exhibiting nearly linear resistivity in temperature and an enhanced pre-factor. Our results provide a clear picture of energy scale evolution relevant to magnetic quantum criticality in UTe$_2$