Superconductivity and disorder inPrOs4Sb12

Abstract

The specific heat, and dc and ac magnetic susceptibility are reported for a large single crystal ofPrOs4Sb12 and,after grinding, its powder. The physical properties of the crystal are typical of the majority of reportedPrOs4Sb12 samples. The room temperature effective paramagnetic moment of the crystal was consistent withthe Pr3+ ionic configuration and full (or nearly full) occupancy of the Pr sublattice. The crystalshowed two distinct anomalies in the specific heat and an overall discontinuity inC/T of approximately1000 mJ K−2 mol−1. The uppertransition (at Tc1) was characteristically rounded. The anomaly atTc2 was very sharp, consistent with a good quality for the crystal. We observed a shoulder inχ′ and two peaksin χ′′ belowTc1. However, there wereno signatures in χ′ of the lower temperature transition. Grinding to powder size smaller than50 µm completely suppresses the upper superconducting transition in boththe specific heat and magnetic susceptibility. It also strongly reducesΔC/Tc atTc2. Stress annealing brings back some of this lostΔC/Tc but does not restore the upper temperature transition. Possible explanations of theexistence of two superconducting specific heat anomalies for single crystals are discussed.