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

TL;DR

This study investigates how pressure influences the coexistence of antiferromagnetism and superconductivity in CeCu2(Si0.98Ge0.02)2, revealing a transition from exotic to heavy-fermion superconductivity and persistent magnetic excitations.

Contribution

It provides new insights into the pressure-induced evolution of coexistent antiferromagnetic and superconducting phases in a Ge-doped CeCu2 compound.

Findings

Antiferromagnetic order is suppressed above 0.19 GPa.

Superconductivity evolves into a heavy-fermion state with a line-node gap above 0.91 GPa.

Persistent low-lying magnetic excitations are observed in the coexistent phase.

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 $T_1T$ = 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.