Effect of impurity scattering on the superconductivity of CeCu2Si2

Abstract

The archetypal heavy fermion superconductor CeCu2Si2 exhibits an unusual pressure–temperature (P–T) phase diagram, in which superconductivity survives over a broad region in pressure (>10 GPa) and the superconducting transition temperature Tc follows a complicated pressure dependence. To understand these unique properties, in this paper, we study a series of Ge-substituted single crystals CeCu2(Si1−xGex)2 (x = 0.01, 0.1 and 0.25). It is found that superconductivity is significantly weakened due to the elevated impurity scattering resulting from the partial Ge/Si substitution. For the sample with x = 0.01, a minimum of Tc(p) is revealed around 3 GPa. Upon further increasing x, the continuous superconducting region in the pure compounds breaks up into two disconnected superconducting domes. Superconductivity vanishes at x ≃ 0.25. These findings suggest that two different superconducting states, one magnetic and the other charge density fluctuations mediated, merge in CeCu2Si2.