123Sb-NQR study of unconventional superconductivity in the filled skutterudite heavy-fermion compound PrOs4Sb12 under high pressure up to P = 3.82 GPa

Abstract

We report ${}^{123}$Sb nuclear quadrupole resonance (NQR) measurements of the filled skutterudite heavy-fermion superconductor PrOs${}_4$Sb${}_{12}$ under high pressure. The temperature dependence of NQR frequency and the spin-lattice relaxation rate $1/T_1$ indicate that the crystal-electric-field splitting ${\Delta }_{\mathrm{CEF}}$ between the ground state ${\Gamma }_1$ singlet and the first excited state ${\Gamma }_4^{(2)}$ triplet decreases with increasing pressure. Ac-susceptibility measurements indicate that the superconducting transition temperature ($T_{\mathrm{c}}$) also decreases with increasing pressure. However, above $P$ $\sim$ 2 GPa, both ${\Delta }_{\mathrm{CEF}}$ and $T_{\mathrm{c}}$ do not depend on external pressure up to $P$ = 3.82 GPa. These pressure dependences of ${\Delta }_{\mathrm{CEF}}$ and $T_{\mathrm{c}}$ suggest an intimate relationship between quadrupole excitations associated with the ${\Gamma }_4^{(2)}$ level and unconventional superconductivity in PrOs${}_4$Sb${}_{12}$. In the superconducting state, 1/$T_1$ below $T_{\mathrm{c}}$ = 1.55 and 1.57 K at $P$ = 1.91 and 2.63 GPa shows a power-law temperature variations and are proportional to $T^5$ at temperatures considerably below $T_{\mathrm{c}}$. These data can be well fitted by the gap model $\Delta (\theta )={\Delta }_0\sin \theta$ with ${\Delta }_0$ = 3.08 $k_{\mathrm{B}}{T}_{\mathrm{c}}$ and 3.04 $k_{\mathrm{B}}{T}_{\mathrm{c}}$ for $P$ = 1.91 and 2.63 GPa, respectively. The results indicate there exists point nodes in the gap function.

6pages, 9figures

References in corpus (3)

• Direct Observation of Quadrupolar Excitons in the Heavy-Fermion Superconductor PrOs${}_4$Sb${}_{12}$
• Eliashberg theory of superconductivity and inelastic rare-earth impurity scattering in filled skutterudite La${}_{1-x}$Pr${}_x$Os${}_4$Sb${}_{12}$
• Impurity induced density of states and residual transport in nonunitary superconductors

Cited by in corpus (1)

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