Exotic superconductivity in the coexistent phase of antiferromagnetism and superconductivity in CeCu2(Si0.98Ge0.02)2: A Cu-NQR study under hydrostatic pressure

Abstract

We report a pressure ($P$) effect on CeCu${}_2$(Si${}_{0.98}$Ge${}_{0.02}$)${}_2$ where an antiferromagnetic (AFM) order at $T_N\sim$ 0.75 K coexists with superconductivity below $T_c\sim$ 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.

5 pages with 4 figures embedded in the text. To be published in J. Phys. Soc. Jpn