Superconductivity has been observed in ${\mathrm{PrOs}}_4{\mathrm{Sb}}_{12}$ at $T_C=1.85\mathrm{}\hspace{0.5em}\mathrm{K}$ and appears to involve heavy fermion quasiparticles with an effective mass $m^{*}\sim 50\hspace{0.5em}{m}_e$ as inferred from the jump in the specific heat at $T_C,$ the upper critical field near $T_C,$ and the normal state electronic specific heat. Thermodynamic and transport measurements suggest that the heavy fermion state has a quadrupolar origin, although a magnetic origin cannot be completely ruled out.

• Received 11 July 2001

DOI:https://doi.org/10.1103/PhysRevB.65.100506