Penetration depth, symmetry breaking, and gap nodes in superconducting PrOs4Sb12

TL;DR

This study investigates the superconducting gap structure of PrOs4Sb12, revealing conflicting evidence for a fully gapped state versus point nodes, and explores the implications of symmetry breaking and TRS in such materials.

Contribution

It provides new insights into the gap symmetry of PrOs4Sb12 by comparing muon spin relaxation and RF measurements, highlighting discrepancies and their relation to TRS breaking.

Findings

Muon spin relaxation suggests a fully gapped spectrum at low T.

RF measurements indicate the presence of point nodes.

Discrepancies are similar to those in TRS-breaking superconductor Sr2RuO4.

Abstract

Transverse-field muon spin relaxation rates in single crystals of the heavy-fermion superconductor PrOs4Sb12 (Tc = 1.85 K) are nearly constant in the vortex state for temperatures below ~0.5Tc. This suggests that the superconducting penetration depth lambda(T) is temperature-independent at low temperatures, consistent with a gapped quasiparticle excitation spectrum. In contrast, radiofrequency measurements yield a stronger temperature dependence of lambda(T), indicative of point nodes in the gap. A similar discrepancy exists in superconducting Sr2RuO4 which, like PrOs4Sb12, breaks time-reversal symmetry (TRS) below Tc, but not in a number of non-TRS-breaking superconductors.