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Heavy-fermion superconductivity and other cooperative effects have been explored by thermal expansion, specific heat and ultrasound measurements on CeCu2Si2 single crystals. Crystals annealed under Cu atmosphere show sharp superconducting transitions at Tcmax = 0.63 K. At the same temperature the "as grown", i.e., non-bulk-superconducting, crystals reveal a pronounced phase-transition anomaly, presumably of structural origin. This new transition is associated with an expansion of the volume upon cooling and gives rise to magnetic correlations. Our results indicate a complex interplay between lattice instability, magnetic phenomena and superconductivity in CeCu2Si2.

We report measurements of (i) the DC magnetization of La1.85Sr0.15CuO4 and YBa2Cu3O7, (ii) thermal properties of La2-xSrxCuO4 (x = 0.15) and (iii) transport properties of YBa2Cu3O7. We arrive at the following results: (i) The shielding magnetization of the sintered pellets studied is dominated by inter-grain Josephson contacts, but we find no evidence for additional intra-grain Josephson contacts. (ii) High-Tc superconductivity is a bulk effect. (iii) For YBa2Cu3O7 the effective mass m* of those carriers involved in the superconducting transition is of the order of 4m0.