Possibility of valence-fluctuation mediated superconductivity in Cd-doped CeIrIn$_5$ probed by In-NQR

TL;DR

This study investigates pressure-induced superconductivity and spin correlations in Cd-doped CeIrIn$_5$, suggesting valence fluctuations may mediate the unconventional superconductivity observed.

Contribution

It provides evidence that valence fluctuations, rather than antiferromagnetic correlations, could be responsible for superconductivity in Cd-doped CeIrIn$_5$ under pressure.

Findings

Superconductivity appears suddenly at specific pressures.

Antiferromagnetism is locally induced by Cd-doping.

Valence change of Ce correlates with superconductivity emergence.

Abstract

We report on a pressure-induced evolution of exotic superconductivity and spin correlations in CeIr(In$_{1-x}$Cd$_{x}$)$_5$ by means of In-Nuclear-Quadrupole-Resonance (NQR) studies. Measurements of an NQR spectrum and nuclear-spin-lattice-relaxation rate $1/T_1$ have revealed that antiferromagnetism induced by the Cd-doping emerges locally around Cd dopants, but superconductivity is suddenly induced at $T_c$ = 0.7 and 0.9 K at 2.34 and 2.75 GPa, respectively. The unique superconducting characteristics with a large fraction of the residual density of state at the Fermi level that increases with $T_c$ differ from those for anisotropic superconductivity mediated by antiferromagnetic correlations. By incorporating the pressure dependence of the NQR frequency pointing to the valence change of Ce, we suggest that unconventional superconductivity in the CeIr(In$_{1-x}$Cd$_{x}$)$_5$ system may be mediated by valence fluctuations.