Abstract
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.
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