Electron Correlations in Superconductor Rh17S15 Studied by 103Rh NMR and Specific Heat Measurements

概要

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The electronic state of superconductor Rh17S15 has been investigated by 103Rh nuclear magnetic resonance (NMR) and specific heat measurements. We have identified the observed NMR lines corresponding to four inequivalent Rh sites in the cubic unit cell and obtained the site-selective information of each site. The spin–lattice relaxation rate $1/T_{1}$ indicates that the $4d$ electrons from the Rh $24m$ site are the most responsible for the large electronic specific heat coefficient $\gamma$. This conclusion is supported by the energy band calculation. Considering the experimental results and the band calculation, we concluded that the $\gamma$ value is enhanced because of the electron correlations of Rh $4d$ bands. In the superconducting state, an exponential decrease of both $1/T_{1}$ and the electron specific heat are observed, revealing the isotropic superconducting gap with $2\Delta/k_{\text{B}}T_{\text{c}}=4.0$. In addition, the decrease of the spin part of the Knight shift indicates the spin-singlet Cooper pair formation. These results demonstrate that Rh17S15 is an $s$-wave superconductor with enhanced effective electron mass.
2010-11-15