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 UTe2 under hydrostatic pressure by magnetoresistivity measurements. In agreement with previous experiments we confirm that superconductivity disappears near a critical pressure p c ≈ 1.5~GPa, and a magnetically ordered state appears. The unusual H c2(T) at low temperatures for H 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 m which is suppressed near p c. The suppression of H m with pressure follows the decrease of temperature T max, at the maximum in the susceptibility along b. The strong reinforcement of H c2 at ambient pressure for H b above 16~T is rapidly suppressed under pressure due to the increase of T sc and the decrease of H m. The change in the hierarchy of the anisotropy of H c2(0) on approaching p c points out that the c axis becomes the hard magnetization axis.