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

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 conlirm that superconductivity disappears near a critical pressure p(c) approximate to 1.5 GPa, and a magnetically ordered state appears. The unusual H-c2(T) at low temperatures for H parallel to 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 neat p(c). The suppression of H-m with pressure follows the decrease of temperature T-chi(max), at the maximum in the susceptibility along b. The strong reinforcement of H-c2 at ambient pressure for H parallel to 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.