Evolution from magnetically ordered to unconventional superconducting phase in a series of CexCu2Si2 compounds: Cu-NQR study

We report that the ground state in a series of CexCu2Si2 compounds evolves from magnetically ordered phase at x = 0.975 to heavy-fermion superconducting (SC) phase at x = 1.025 based on Cu-NQR measurements. We found that the x = 0.99 sample does not exhibit any long-range phase transition, but is dominated by critical magnetic fluctuations with very low frequencies comparable to the NQR frequency which develop rapidly below Tm ∼ 1.2 K. For the x = 1.00 and 1.25 samples such the state is expelled by the onset of the SC state. We suggest that this evolution from the magnetic to the SC state is driven by the effective tuning of chemical potential with varying the Ce-nominal content x. (author)