Superconductivity in CeCu2Si2 (invited)

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Abstract
The specific heat, dc magnetization, and resistivity have been measured on a number of samples of CeCu2Si2, which was previously found to assume a novel superconducting state below 0.5 K [F. Steglich et al., Phys. Rev. Lett. 43, 1892 (1979)]. By comparing the transition temperatures of samples which have undergone different heat treatments, we demonstrate that small fractions of spurious phases hinder the onset of superconductivity but are gradually removed with annealing. With a very pure sample obtained in this way, we have fully confirmed all the characteristics of the superconducting phase transition reported before on less pure samples. However, even after this heat treatment, the samples show clear signs of striking inhomogeneities, manifested by a static Meissner effect of bulk samples representing typically only a few percent of the volume. An increase of this Meissner signal up to 60 vol% is observed after powdering the samples. In addition to measurements in the superconducting state, the intrinsic value of the low-temperature susceptibility in the normal state was determined by measurements on a pure sample and is discussed in connection with the large electronic specific-heat coefficient γ.