Anisotropy of the Upper Critical Field in the Heavy-Fermion Superconductor UTe2 under Pressure

Abstract

We studied the anisotropy of the superconducting upper critical field $H_{c2}$ in the heavy-fermion superconductor UTe${}_2$ under hydrostatic pressure by magnetoresistivity measurements. In agreement with previous experiments we confirm that superconductivity disappears near a critical pressure $p_{\mathrm{c}}\approx 1.5$~GPa, and a magnetically ordered state appears. The unusual $H_{c2}(T)$ at low temperatures for $H\parallel a$ suggests that the multiple superconducting phases which appear under pressure have quite different $H_{c2}$. For a field applied along the hard magnetization $b$ axis $H_{c2}(0)$ is glued to the metamagnetic transition $H_{\mathrm{m}}$ which is suppressed near $p_{\mathrm{c}}$. The suppression of $H_{\mathrm{m}}$ with pressure follows the decrease of temperature $T_{\ddot{I}}{‡}^{\max }$, at the maximum in the susceptibility along $b$. The strong reinforcement of $H_{c2}$ at ambient pressure for $H\parallel b$ above 16~T is rapidly suppressed under pressure due to the increase of $T_{\mathrm{sc}}$ and the decrease of $H_{\mathrm{m}}$. The change in the hierarchy of the anisotropy of $H_{c2}(0)$ on approaching $p_{\mathrm{c}}$ points out that the $c$ axis becomes the hard magnetization axis.

5 pages and 4 figures, supplemental material: 9 figures