Enhancement of Superconducting Transition Temperature in CeCu ₂Ge ₂ under High Pressures

Enhancement of superconducting transition temperature T _c is confirmed at around 16 GPa in the pressure-induced superconductor CeCu ₂Ge ₂. The superconducting H _c - T _c phase diagrams at the low-T _c and high-T _c pressure regions indicates that the heavy quasi particles form the singlet Cooper pairs. At both low-T _c and high-T _c pressure regions, Fermi liquid behavior of p ∼ AT ² is observed only at low temperatures below 1 K in the normal state induced by the external field above H _c2. At 21 GPa where the superconductivity disappears down to 50 mK, the temperature region following ρ ∼ AT ² increases drastically up to 40 K and the coefficient A decreases rapidly. These results indicate that the strongly correlated electrons are responsible essentially for the appearance of superconductivity in this system.