On the nature of two superconducting transitions in the specific heat of PrOs$_4$Sb$_{12}$: Effects of crystal grinding

TL;DR

This study investigates the dual superconducting transitions in PrOs$_4$Sb$_{12}$, revealing their sensitivity to crystal grinding and suggesting a characteristic length scale for the higher temperature phase.

Contribution

It demonstrates that grinding suppresses the upper superconducting transition and proposes a length scale of about 100 μm for the higher temperature phase.

Findings

Grinding suppresses the upper transition in specific heat and susceptibility.

Two distinct anomalies are observed in specific heat, with the upper transition being rounded and the lower sharp.

The higher temperature superconducting phase has a characteristic length scale of approximately 100 μm.

Abstract

Specific heat, dc- and ac-magnetic susceptibility are reported for a large single crystal of PrOs$_4$Sb$_{12}$ and, after grinding, its powder. The room temperature effective paramagnetic moment of the crystal was consistent with the Pr$^{3+}$ ionic configuration and full occupancy of the Pr-sublattice. The crystal showed two distinct anomalies in the specific heat and an overall discontinuity in $C/T$ of more than 1000 mJ/K$^2$mol. The upper transition (at $T_{c1}$) was rounded, in an agreement with previous reports. The anomaly at $T_{c2}$ was very sharp, consistent with a good quality of the crystal. We observed a shoulder in $\chi$' and two peaks in $\chi$'' below $T_{c1}$. However, there were no signatures in $\chi$' of the lower temperature transition. PrOs$_4$Sb$_{12}$ is extremely sensitive to grinding, which suppresses the upper superconducting transition in both the specific heat and magnetic susceptibility. $\Delta C/T_{c}$ was reduced to 140 mJ/K$^2$ mol in the powdered sample. Existing data on ground, polished, and sliced crystals suggests the existence of a length scale of order 100 $\mu$, characterizing the higher temperature superconducting phase.