Drastic change in magnetic anisotropy of UTe2 under pressure revealed by 125Te-NMR

TL;DR

This study uses 125Te-NMR measurements to reveal a significant change in magnetic anisotropy and Fermi surface properties of UTe2 under pressure, correlating with the suppression of superconductivity and emergence of magnetic order.

Contribution

It provides new insights into the pressure-induced electronic and magnetic phase transitions in UTe2, highlighting the abrupt Fermi surface change at the critical pressure.

Findings

T_chimax decreases and vanishes at Pc=1.7 GPa

Heavy-fermion state exists below Pc, absent above

Superconductivity only in the heavy-fermion phase

Abstract

To investigate the normal-state magnetic properties of UTe2 under pressure, we perform 125Te nuclear magnetic resonance (NMR) measurements up to 2 GPa. Below 1.2 GPa, the b-axis NMR Knight shift shows a broad maximum at the so-called T_chimax on cooling, which is consistent with the magnetization measurement under pressure. T_chimax decreases with increasing pressure and disappears at the critical pressure Pc = 1.7 GPa, above which superconductivity is destroyed. This tendency is also observed in the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1. At low pressures, 1/T1 shows a conventional Fermi-liquid behavior (1/T1T = constant) at low temperatures, indicating the formation of the heavy-fermion state. Above Pc, 1/T1T follows a 1/T behavior without any crossover to the heavy-fermion state down to the lowest temperature (~3 K). In addition, the NMR signals disappear below 3~K, due to the influence of the magnetically ordered moments. From the pressure dependence of the T_chimax and Knight shift, it was found that the Fermi surface character is abruptly changed at Pc, and that superconductivity is observed only in the heavy-fermion state.