Exotic Superconductivity in the Coexistent Phase of Antiferromagnetism and Superconductivity in CeCu2(Si0.98Ge0.02)2: A Cu-NQR Study under Hydrostatic Pressure

We report a pressure ( P ) effect on CeCu 2 (Si 0.98 Ge 0.02 ) 2 where an antiferromagnetic (AFM) order at T N ∼0.75 K coexists with superconductivity below T c ∼0.4 K. At pressures exceeding P = 0.19 GPa, the AFM order is suppressed, which demonstrates that the sudden emergence of AFM order due to the Ge doping is ascribed to the intrinsic lattice expansion. The exotic superconductivity at P = 0 GPa is found to evolve into a typical heavy-fermion one with a line-node gap above P = 0.91 GPa. We highlight that the anomalous enhancement in nuclear spin–lattice relaxation rate 1/ T 1 that follows a T 1 T = const. behavior well below T c at P = 0 GPa is characterized by the persistence of low-lying magnetic excitations, which may be inherent to the coexistent state of antiferromagnetism and superconductivity.