Evidence for time-reversal symmetry breaking in superconductingPrPt4Ge12

Abstract

Zero-and longitudinal-field muon-spin-rotation ͑SR͒ experiments were performed on the superconductors PrPt 4 Ge 12 and LaPt 4 Ge 12 . In PrPt 4 Ge 12 below T c a spontaneous magnetization with a temperature variation resembling that of the superfluid density appears. This observation implies time-reversal symmetry ͑TRS͒ breaking in PrPt 4 Ge 12 below T c = 7.9 K. This remarkably high T c for an anomalous superconductor and the weak and gradual change in T c and of the related specific-heat anomaly upon La substitution in La 1−x Pr x Pt 4 Ge 12 suggests that the TRS breaking is due to orbital degrees of freedom of the Cooper pairs.

Comparative photoemission studies on the superconducting gap of the filled skutterudite superconductors LaPt4Ge12and PrPt4Nakamura1, Okazaki2, Yoshida3 et al. 2012Phys. Rev. B246221View full textAdd to dashboardCite

“…If one of the two bands is related to the presence of spontaneous magnetization in PrPt 4 Ge 12 and vanishes with the substitution of La, it may explain the smooth variation in the spontaneous magnetization as a function of La concentration in Pr x La 1−x Pt 4 Ge 12 observed in μSR measurements. 9 This study has suggested one possible explanation based our experimental data; to confirm the multiband superconductivity in PrPt 4 Ge 12 , further experimental studies are necessary.…”

“…8 Previous comparative zero-and longitudinal-field μSR experiments on PrPt 4 Ge 12 and LaPt 4 Ge 12 reported spontaneous magnetization with a temperature variation resembling that of the superfluid density below T c only for PrPt 4 Ge 12 , implying time-reversal symmetry breaking in PrPt 4 Ge 12 . 9 While these studies have suggested unconventional superconductivity of PrPt 4 Ge 12 , very recent studies of the 73 Ge-nuclear quadrupole resonance (NQR) showed a coherence peak just below T c , indicating that the superconductivity is accounted for in terms of the conventional BCS regime. 10 In order to understand the anomalous superconducting properties of PrPt 4 Ge 12 , it is crucial to directly observe the superconducting gap.…”

Superconducting gap structure of the skutteruditeLaPt4Ge12probed by specific heat and thermal transport

“…Additionally, a number of investigations including photoemission, magnetization, penetration depth, and specific heat revealed multiband superconductivity in this compound 13,[16][17][18][19] . The continuous evolution of T c across the doping series (Pr 1−x La x )Pt 4 Ge 12 suggests compatible order parameters of the end members PrPt 4 Ge 12 and LaPt 4 Ge 12 14 . However, the few existing investigations on LaPt 4 Ge 12 point towards a single isotropic gap: the specific-heat jump ∆C/γ n T c is only slightly above the BCS value suggesting a weaker coupling than in PrPt 4 Ge 12 8 .…”

Weak interband-coupling superconductivity in the filled skutteruditeLaPt4Ge12

“…Furthermore, a coherence peak was revealed in the nuclear spin-lattice relaxation rate 1/T 1 just below T c for PrPt 4 Ge 12 , which is unexpectedly suppressed in LaPt 4 Ge 12 [17]. However, the weak variation of T c and of the specific heat jump at T c with the Pr-content x in La 1−x Pr x Pt 4 Ge 12 suggests that the order parameters of the two end members are compatible [12] In this Letter, we report a comprehensive study of the magnetic penetration depth λ(T, B) and superfluid density ρ s (T ) of LaPt 4 Ge 12 by using a µSR experiment and a TDO-based technique. The London penetration depth λ L (T ), measured by the TDO method, follows exponential-type behavior in the low-temperature limit, suggesting nodeless superconductivity for LaPt 4 Ge 12 .…”

“…Resembling those of PrOs 4 Sb 12 , zero-field µSR experiments showed evidence of time-reversal symmetry (TRS) breaking in the superconducting state of PrPt 4 Ge 12 , but not for LaPt 4 Ge 12 [11][12][13]. However, more recent experiments suggested multi-gap SC for PrPt 4 Ge 12 [14][15][16].…”