Anisotropic superconductivity and unusually robust electronic critical field in single crystal La$_{7}$Ir$_{3}$

TL;DR

This study reports the successful growth of high-quality single crystals of La$_{7}$Ir$_{3}$, revealing anisotropic superconducting properties and a robust electronic critical field indicative of surface superconductivity, advancing understanding of its pairing mechanism.

Contribution

First demonstration of high-quality single crystals of La$_{7}$Ir$_{3}$ and detailed investigation of their anisotropic superconducting properties and surface superconductivity phenomena.

Findings

Anisotropic lower and upper critical fields observed.

Presence of a robust electronic critical field diverging from heat capacity measurements.

Evidence of surface superconductivity in 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.