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

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 $T_{\mathrm{c}}$ and the energy gap ${\Delta }_0$ increase drastically from $T_{\mathrm{c}}=0.4$ K and $2{\Delta }_0/k_{\mathrm{B}}{T}_{\mathrm{c}}=5$ in CeIrIn${}_5$ up to $T_{\mathrm{c}}=1.2$ K and $2{\Delta }_0/k_{\mathrm{B}}{T}_{\mathrm{c}}=8.3$ 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.

4pages,5figures,to appear in Phys. Rev. Lett

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