Composition dependence of the superconducting properties of UTe₂

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 T c 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*/γ N, 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.

Multicomponent superconducting order parameter in UTe 2

“…Finally, recent work has shown that there are two well-separated transitions under pressure (29,30), which supports the idea that there are two nearly degenerate symmetry breaking possibilities for a superconducting state in UTe2. Both studies show that the splitting diminishes rapidly with decreasing pressure, with one study confirming the existence of splitting at ambient pressure (30), suggesting that the small splitting evident in our heat capacity experiments may be sensitive to sample quality and difficult to discern in other published work (2,31).…”

Comparison of two superconducting phases induced by a magnetic field in UTe2

“…An alternative picture without phase transition between SC1 and SC2 cannot be excluded, since the upturn of H c2 could result from a tight balance between the orbital limitation and the increase of the coupling λ with field 37 . We further note that, at ambient pressure and zero magnetic field, a single superconducting transition was identified in 23,24,40 but two separated superconducting transitions were reported in 28,41 . Figure 1(b) presents a combination of low-temperature magnetic-field versus field-angle phase diagrams of UTe 2 obtained by Ran et al 33 and Knebel et al 37 It summarizes the effect of magnetic fields applied in the (a, b) and (b, c) planes.…”

Effect of uranium deficiency on normal and superconducting properties in unconventional superconductor UTe$_2$

“…The sample dependence on superconductivity and chemical composition is extensively studied in ref. [23] and a significant difference in composition ratio Te/U is reported between superconducting and non-superconducting samples, where the nonsuperconducting sample shows systematically larger Te/U ratio.…”

“…[21,22] As inferred from the absence of superconductivity in single crystals used for earlier studies, relatively small lattice imperfection has strong impact on physical properties. Even in superconducting samples, superconducting transition temperature varies from about 1.5 K up to 2 K [18,23,24]. Previous study proposed that the emergence of superconductivity would be caused by slight Te-deficiency [23].…”

“…Even in superconducting samples, superconducting transition temperature varies from about 1.5 K up to 2 K [18,23,24]. Previous study proposed that the emergence of superconductivity would be caused by slight Te-deficiency [23]. Yet, the relationship between such non-stoichiometry and physical properties has not been clarified.…”