Enhancing the Superconducting Transition Temperature due to Strong-Coupling Effect under Antiferromagnetic Spin Fluctuations in CeRh1-xIrxIn5 : 115In-NQR Study

TL;DR

This study demonstrates that antiferromagnetic spin fluctuations near a quantum critical point enhance the superconducting transition temperature and energy gap in heavy-fermion compounds CeRh$_{1-x}$Ir$_{x}$In$_5$, revealing a strong-coupling mechanism.

Contribution

It provides experimental evidence linking antiferromagnetic spin fluctuations to increased $T_c$ and strong-coupling superconductivity in CeRh$_{1-x}$Ir$_{x}$In$_5$, highlighting the role of quantum criticality.

Findings

Superconducting transition temperature $T_c$ increases with Rh content.

Antiferromagnetic spin fluctuations develop near the AFM quantum critical point.

Energy gap $$ increases, indicating strong-coupling superconductivity.

Abstract

We report on systematic evolutions of antiferromagnetic (AFM) spin fluctuations and unconventional superconductivity (SC) in heavy-fermion (HF) compounds CeRh$_{1-x}$Ir$_{x}$In$_5$ via $^{115}$In nuclear-quadrupole-resonance (NQR) experiment. The measurements of nuclear spin-lattice relaxation rate $1/T_1$ have revealed the marked development of AFM spin fluctuations as a consequence of approaching an AFM ordered state with increasing Rh content. Concomitantly the superconducting transition temperature $T_{\rm c}$ and the energy gap $\Delta_0$ increase drastically from $T_{\rm c} = 0.4$ K and $2\Delta_0/k_{\rm B}T_{\rm c} = 5$ in CeIrIn$_5$ up to $T_{\rm c} = 1.2$ K and $2\Delta_0/k_{\rm B}T_{\rm c} = 8.3$ in CeRh$_{0.3}$Ir$_{0.7}$In$_5$, respectively. The present work suggests that the AFM spin fluctuations in close proximity to the AFM quantum critical point are indeed responsible for the onset of strong-coupling unconventional SC with the line node in the gap function in HF compounds.