Dependence of the superconducting transition temperature and lattice parameter on hydrostatic pressure for Rb 3C 60

Abstract

The equation of state (EOS) of polycrystalline Rb 3C 60 was accurately determined to 1 GPa at 295 K and 14 K using high-pressure neutron diffraction. In a separate experiment on Rb 3C 60, the variation of the superconducting transition temperature T c with hydrostatic pressure was also measured. The resulting dependence of T c on lattice parameter a is almost linear, with initial slope dT c dlna ∼- +520 K , but is less steep than the T c ( a)-dependence obtained at ambient pressure if Rb is substituted with smaller alkali metal cations. T c ( a) for Rb 3C 60 thus does not follow a universal curve in high pressure and substitution experiments, as previously claimed. Starting with the measured EOS at room temperature, we use a Debye model to estimate the Murnaghan EOS for both NaCl (used here as a pressure calibrant) and Rb 3C 60 over the entire temperature region below 400 K.