Pressure Tuning of Superconductivity of LaPt4Ge12 and PrPt4Ge12 Single Crystals

We carried out electrical resistivity and X-ray diffraction (XRD) studies on the filled skutterudite superconductors LaPt4Ge12 and PrPt(4)Ge(12 )under hydrostatic pressure. The superconducting transition temperature T-c is linearly suppressed upon increasing pressure, though the effect of pressure on T-c is rather weak. From the analysis of the XRD data, we obtain bulk moduli of B = 106 GPa and B = 83 GPa for LaPt4Ge12 and PrPt4Ge12, respectively. The knowledge of the bulk modulus allows us to compare the dependence of T-c on the unit-cell volume from our pressure study directly with that found in the substitution series La1-xPrxPt4Ge12. We find that application of hydrostatic pressure can be characterized mainly as a volume effect in LaPt4Ge12 and PrPt4Ge12, while substitution of Pr for La1-xPrxPt4Ge12 yields features going beyond a simple picture.