Exotic magnetic and superconducting phases in CeCu2Si2 close to magnetically ordered state : Cu-NQR study

Abstract We report Cu-NQR results under pressure on heavy-fermion (HF) superconductor CeCu 2 Si 2 close to a magnetic phase, Ce 0.99 Cu 2.02 Si 2 and CeCu 2 (Si 0.98 Ge 0.02 ) 2 . It is found that an application of a minute pressure exceeding 0.3 GPa markedly suppresses low-energy magnetic fluctuations observed at ambient pressure ( P =0) in Ce 0.99 Cu 2.02 Si 2 . Correspondingly, anomalous superconducting (SC) characteristics evolve into conventional HF-SC ones with increasing pressure. In the latter, the Ge substitution works as a negative chemical pressure. CeCu 2 (Si 0.98 Ge 0.02 ) 2 reveals a magnetic phase transition at T N =0.75 K followed by the SC phase transition at T c ∼0.4 K at P =0. It is suggested experimentally that the magnetic fluctuations seen in Ce 0.99 Cu 2.02 Si 2 at P =0 possesses a quantum critical character of both SC and magnetically ordered states.