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 CeCu₂(Si0.98Ge0.02)₂ where an antiferromagnetic (AFM) order at TN ~ 0.75 K coexists with superconductivity below Tc ~ 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/T₁ that follows a T₁T = const. behavior well below Tc 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.