Suppression of time reversal symmetry breaking superconductivity in Pr(Os,Ru)_4Sb_12 and (Pr,La)Os_4Sb_12

TL;DR

This study investigates how doping with Ru or La affects the breaking of time-reversal symmetry in certain superconductors, revealing that Ru suppresses TRS more efficiently than La, supporting an excitonic pairing mechanism.

Contribution

It provides experimental evidence on how Ru and La doping influence TRS-breaking in Pr-based superconductors, highlighting the different suppression efficiencies and supporting a specific pairing mechanism.

Findings

Ru doping suppresses TRS more rapidly than La doping

TRS persists at high La concentrations but not with Ru above x ~ 0.6

Data supports a crystal-field excitonic Cooper pairing mechanism

Abstract

Zero-field muon spin relaxation experiments have been carried out in the Pr(Os_{1-x}Ru_x)_4Sb_12 and Pr_{1-y}La_yOs_4Sb_12 alloy systems to investigate broken time-reversal symmetry (TRS) in the superconducting state, signaled by the onset of a spontaneous static local magnetic field B_s. In both alloy series B_s initially decreases linearly with solute concentration. Ru doping is considerably more efficient than La doping, with a ~50% faster initial decrease. The data suggest that broken TRS is suppressed for Ru concentration x >~ 0.6, but persists for essentially all La concentrations. Our data support a crystal-field excitonic Cooper pairing mechanism for TRS-breaking superconductivity.