Magnetic Properties under Pressure in Novel Spin-Triplet Superconductor UTe2

Abstract

We report the magnetic susceptibility and the magnetization under pressures up to 1.7 GPa above the critical pressure, P c ∼ 1.5 GPa, for H a, b and c-axes in the novel spin triplet superconductor UTe 2 . The anisotropic magnetic susceptibility at low pressure with the easy magnetization a-axis changes to the quasi-isotropic behavior at high pressure, revealing a rapid suppression of the susceptibility for a-axis, and a gradual increase of the susceptibility for the b-axis. At 1.7 GPa above P c , magnetic anomalies are detected at T MO ∼ 3 K and T WMO ∼ 10 K. The former anomaly corresponds to long-range magnetic order, most likely antiferromagnetism, while the latter shows a broad anomaly, which is probably due to the development of short range order. The unusual decrease and increase of the susceptibility below T WMO for H a and b-axes, respectively, indicate the complex magnetic properties at low temperatures above P c . This is related to the interplay between multiple fluctuations dominated by antiferromagnetism, ferroamgnetism, valence and Fermi surface instabilities.

Thermodynamic signatures of short-range magnetic correlations in UTe$_2$

“…These data predict a suppression of T * , as well as a switching of the magnetic hard direction from the b axis to the c-axis, under c-axis uniaxial pressure. This is line with recent magnetization measurements under hydrostatic pressure [20], probably because the largest uniaxial pressure effect (see Fig. 1a) is along the c-axis.…”

“…The monotonic temperature dependence of Γ e and in particular the absence of an anomalous behavior at T * suggests a single energy scale responsible for both T * and γ. Using equation (1) and Γ e | 12K = −16 we find ∂T * /∂p = -4 K/GPa and hence a suppression of T * to 0 around p = 3 GPa in agreement with recent transport [18] and also magnetization measurements [20] where this transition is observed at p ≈ 1.5 GPa. Our value of Γ e is close in amplitude and sign to Γ H = −21 related to the metamagnetic field from Ref.…”

“…From our thermodynamic data, we calculate the electronic Grüneisen parameter related to T * . It is found to be comparable in magnitude to that of the metamagnetic field [20] indicating a common origin. Finally, enhanced Wilson and Korringa ratios suggest that the existence of short range ferromagnetic fluctuations cannot be ruled out, although no direct evidence for their existence has been found to date.…”

Spatially inhomogeneous superconductivity in UTe2

“…This has previously been claimed based on the fact that H c2 becomes largest along the c axis near 1.5 GPa 12 . More recently, it was experimentally confirmed via susceptibility measurements under pressure 15 . The magnetic interactions at high pressure are quite different from those at low pressure, which explains the emergence of two magnetic transitions and antiferromagnetic order.…”

“…The magnetic interactions at high pressure are quite different from those at low pressure, which explains the emergence of two magnetic transitions and antiferromagnetic order. In fact, the b axis becomes the easy axis in the magnetically ordered state 15 . We also highlight the possibility that samples from different batches may exhibit different magnetic properties even at ambient pressure.…”