Anisotropic superconductivity and unusually robust electronic critical field in single crystal La${}_7$Ir${}_3$

Abstract

Polycrystalline La${}_7$Ir${}_3$ is reported to show superconductivity breaking time-reversal symmetry while also having an isotropic $s$-wave gap. Single crystals of this noncentrosymmetric superconductor are highly desirable to understand the nature of the electron pairing mechanism in this system. Here we report the growth of high-quality single crystals of La${}_7$Ir${}_3$ by the Czochralski method. The structural and superconducting properties of these large crystals have been investigated using x-rays, magnetization, resistivity and heat capacity measurements. We observe a clear anisotropy in the lower and upper critical fields for magnetic fields applied parallel and perpendicular to the hexagonal $c$ axis. We also report the presence of a robust electronic critical field, that diverges from the upper critical field derived from heat capacity, which is the hallmark of surface superconductivity.

20 + 5 pages, 6 + 4 figures, 1 + 1 tables. Accepted for publication into Physical Review Materials

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