Evidence for time-reversal symmetry breaking in superconducting PrPt4Ge12

TL;DR

This study provides evidence that the superconductor PrPt4Ge12 exhibits time-reversal symmetry breaking below its critical temperature, likely due to orbital degrees of freedom of Cooper pairs, marking a significant finding in unconventional superconductivity.

Contribution

The paper reports the first muSR evidence of TRS breaking in PrPt4Ge12, highlighting its high Tc and suggesting a novel orbital mechanism behind the symmetry breaking.

Findings

TRS breaking observed below Tc in PrPt4Ge12

High superconducting transition temperature of 7.9 K

TRS breaking linked to orbital degrees of freedom

Abstract

Zero and longitudinal field muon spin rotation (muSR) experiments were performed on the superconductors PrPt4Ge12 and LaPt4Ge12. In PrPt4Ge12 below Tc a spontaneous magnetization with a temperature variation resembling that of the superfluid density appears. This observation implies time-reversal symmetry (TRS) breaking in PrPt4Ge12 below Tc = 7.9 K. This remarkably high Tc for an anomalous superconductor and the weak and gradual change of Tc and of the related specific heat anomaly upon La substitution in La_(1-x)Pr_xPt_4Ge_(12) suggests that the TRS breaking is due to orbital degrees of freedom of the Cooper pairs.