A new heavy fermion superconductor:: The filled skutterudite compound PrOs4Sb12

The filled skutterudite compound PrOs4Sb12 exhibits superconductivity below a critical temperature T-c = 1.85 K that develops out of a nonmagnetic heavy Fermi liquid with an effective mass m* approximate to 50 m(e), where m(e) is the free electron mass. Analysis of magnetic susceptibility, specific heat, electrical resistivity and inelastic neutron scattering measurements within the context of a cubic crystalline electric field yields a Pr3+ energy level scheme that consists of a Gamma(3) nonmagnetic doublet ground state that carries an electric quadrupole moment, a low lying Gamma(5) triplet excited state at similar to 10 K, and Gamma(4) triplet and Gamma(1) singlet excited states at much higher temperatures. The superconducting state appears. to be unconventional and to consist of two distinct superconducting phases. An ordered phase of magnetic or quadrupolar origin occurs at high fields and low temperatures, suggesting that the superconductivity may occur in, the vicinity of a magnetic or electric quadrupolar quantum critical point.