Composition dependence of the superconducting properties of UTe2

Luke Pritchard Cairns,Christopher D O'Neill,Andrew Huxley,Callum R Stevens

doi:10.1088/1361-648x/ab9c5d

Luke Pritchard Cairns, Christopher D O'Neill + Show 2 more

Open Access

https://doi.org/10.1088/1361-648x/ab9c5d

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Abstract

A better understanding of the synthesis conditions, composition and physical properties of UTe2 are required to interpret previously reported unconventional superconductivity. Here we report how the superconducting properties of single crystals depend on the ratio of elements present in their synthesis by chemical vapour transport. We have obtained crystals with the highest reported ambient pressure Tc and a larger superconducting heat capacity jump from a growth with a U:Te ratio different from that widely used in the literature. For these crystals, the ratio of residual heat capacity in the superconducting state to that of the normal state, γ*/γN, is significantly lower than 0.5, reported elsewhere. An upturn in the heat capacity below 200 mK is also reduced compared to other studies and is well described by a Schottky anomaly and residual Sommerfeld term rather than quantum critical behaviour.

Highlights

The discovery of unconventional superconductivity in the heavy-fermion paramagnet UTe2 sparked a whirlwind of activity
A splitting of Tc has been observed in the heat capacity at ambient pressure [11], it is unclear whether the two splittings have a common origin
We have demonstrated that, for an intermediate starting ratio, the superconducting transition temperature, and the specific heat jump at this transition, are enhanced beyond any values observed previously

Summary

INTRODUCTION

The discovery of unconventional superconductivity in the heavy-fermion paramagnet UTe2 sparked a whirlwind of activity. The majority of specific heat studies observe a residual Sommerfeld coefficient, γ∗, within the superconducting state [8, 9, 12], something which has been interpreted as evidence for non-unitary pairing [1]. The magnitude of this residual contribution is typically measured to be approximately half of the normal state value, γN , leading some studies to suggest that only one of the two spin directions is paired in the superconducting state [2]. The fact that γ∗/γN is significantly lower than 0.5 in our higher Tc samples argues against the interpretation that only one spin direction is paired

Sample synthesis

Energy dispersive X-ray analysis

Specific Heat

DISCUSSION