Pronounced enhancement of the lower critical field and critical current deep in the superconducting state of PrOs$_4$Sb$_{12}$

TL;DR

This study reports an unexpected enhancement of the lower critical field and critical current deep within the superconducting state of PrOs$_4$Sb$_{12}$, suggesting a phase transition below 0.3 T/Tc that correlates with anomalies in other physical properties.

Contribution

The paper presents evidence of a possible new superconducting phase transition in PrOs$_4$Sb$_{12}$ occurring below 0.3 T/Tc, based on critical field and current measurements.

Findings

Enhanced $H_{c1}(T)$ and $I_{c}(T)$ below 0.6 K

Correlation with anomalies in other physical properties

Comparison with heavy fermion superconductors

Abstract

We have observed an unexpected enhancement of the lower critical field $H_{c1}(T)$ and the critical current $I_{c}(T)$ deep in the superconducting state below $T \approx 0.6$ K ($T/T_{c} \approx 0.3$) in the filled skutterudite heavy fermion superconductor PrOs$_4$Sb$_{12}$. From a comparison of the behavior of $H_{c1}(T)$ with that of the heavy fermion superconductors U$_{1-x}$Th$_x$Be$_{13}$ and UPt$_3$, we speculate that the enhancement of $H_{c1}(T)$ and $I_{c}(T)$ in PrOs$_4$Sb$_{12}$ reflects a transition into another superconducting phase that occurs below $T/T_{c} \approx 0.3$. An examination of the literature reveals unexplained anomalies in other physical properties of PrOs$_4$Sb$_{12}$ near $T/T_{c} \approx 0.3$ that correlate with the features we have observed in $H_{c1}(T)$ and $I_{c}(T)$.