Towards an understanding of the intrinsic properties in UTe₂

UTe₂ has attracted much recent interest as a possible spin-triplet topological superconductor. With improvements in sample quality [1, 2], it has become increasingly important to understand which properties of UTe2 are intrinsic and which arise from disorder or impurities. Here, we show via thermal expansion and specific heat measurements that the double transition in some UTe2 samples arises from sample inhomogeneity [3]. We will also discuss how growing under optimal conditions reliably results in single crystals with both a higher Tc and a single transition [1]. Pressure studies on these improved crystals reveal that the single transition splits into two transitions near 0.3 GPa. For crystals that show a double transition at ambient pressure, we observe a double transition at all superconducting transitions in the phase diagram [4]. This provides further support that the double transition arises from sample inhomogeneity. Finally, we note a correspondence between the residual gamma in specific heat and the superconducting transition temperature, indicating that the residual gamma is likely arising from impurities [3, 5, 6].

[1] P.F.S. Rosa et al., Communications Materials 3, 33 (2022).

[2] H. Sakai et al., Phys. Rev. Materials 6, 073401 (2022).

[3] S.M. Thomas et al., Phys. Rev. B 104, 224501 (2021).

[4] Erratum to S.M. Thomas et al., Science advances 6, eabc8709 (2020).

[5] L.P. Cairns et al., J. Phys.: Condens. Matter 32, 415602 (2020).

[6] D Aoki et al., J. Phys.: Condens. Matter 34, 243002 (2022).