Maki Parameter and Upper critical Field of the Heavy-Fermion Superconductor UBe13

TL;DR

This study investigates the superconducting properties of UBe13, revealing isotropic upper critical fields, point nodes in the gap, and a decreasing Maki parameter, providing insights into its pairing symmetry and paramagnetic effects.

Contribution

It presents new low-temperature specific heat measurements and critical field data for UBe13, highlighting isotropic behavior and the temperature dependence of the Maki parameter.

Findings

Superconducting transition at an intermediate temperature.

T^3 behavior of specific heat indicating point nodes.

Isotropic upper critical fields down to 0.5 K.

Abstract

We have performed low-temperature specific-heat measurements in magnetic fields for a single crystal UBe13. It has been observed that our sample exhibits a superconducting transition at an intermediate temperature between previously reported values for two variant samples called H type and L type. The specific heat C(T) of our sample shows a T^3 behavior in the temperature range below 0.7 Tc, which is similar to the behavior of the H-type sample, suggesting the existence of point nodes in the superconducting gap function. We have obtained the upper-critical-field curves Hc2 for the [001], [110], and [111] crystal axes, which show no anisotropy at least down to the lowest measured temperature of 0.5 K. We have also derived the Maki parameter kappa2, and it has been revealed that the kappa2 steeply decreases isotropically upon cooling just below Tc. Paramagnetic effects and the symmetry of Cooper pairing of UBe13 are discussed.