Fermi-Surface Instability in the Heavy-Fermion Superconductor UTe2

Transport measurements are presented up to fields of 29 T in the recently discovered heavy-fermion superconductor UTe2 with magnetic field H applied along the easy magnetization a axis of the body-centered orthorhombic structure. The thermoelectric power varies linearly with temperature above the superconducting transition, TSC=1.5 K, indicating that superconductivity develops in a Fermi liquid regime. As a function of field the thermoelectric power shows successive anomalies which appear at critical values of the magnetic polarization. Remarkably, the lowest magnetic field instability for H∥a occurs for the same critical value of the magnetization (0.4 μB) than the first order metamagnetic transition at 35 T for field applied along the b axis. It can be clearly identified as a Lifshitz transition. The estimated number of charge carriers at low temperature reveals a metallic ground state distinct from LDA calculations indicating that strong electronic correlations are a major issue.