Quasiparticle Excitations and Evidence for Superconducting Double Transitions in Monocrystalline U0.97Th0.03Be13

TL;DR

This study investigates the superconducting gap symmetry and magnetic response of U0.97Th0.03Be13, revealing evidence for two distinct superconducting phases and their transition characteristics through heat capacity and magnetization measurements.

Contribution

It provides new experimental evidence for double superconducting transitions and clarifies the gap symmetry in U0.97Th0.03Be13, advancing understanding of its complex superconducting state.

Findings

Identification of two distinct superconducting phases

Observation of isotropic Tc2(H) transition

Fully opened superconducting gap below Tc2

Abstract

Superconducting (SC) gap symmetry and magnetic response of cubic U0.97Th0.03Be13 are studied by means of high-precision heat-capacity and dc magnetization measurements using a single crystal, in order to address the long-standing question of its second phase transition at Tc2 in the SC state below Tc1. The absence (presence) of an anomaly at Tc2 in the field-cooling (zero-field-cooling) magnetization indicates that this transition is between two different SC states. There is a qualitative difference in the field variation of the transition temperatures; Tc2(H) is isotropic whereas Tc1(H) exhibits a weak anisotropy between [001] and [111] directions. In the low temperature phase below Tc2(H), the angle-resolved heat-capacity $C(T,H, \phi)$ reveals that the gap is fully opened over the Fermi surface, narrowing down the possible gap symmetry.