Evidence for Point Nodes in the Superconducting Gap Function in the Filled Skutterudite Heavy-Fermion Compound PrOs_4Sb_<12> : ^<123>Sb-NQR Study under Pressure(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We report ^<123>Sb nuclear quadrupole resonance (NQR) measurements of the filled skutterudite heavy-fermion superconductor PrOs_4Sb_<12> under high pressures of 1.91 and 2.34 GPa. The temperature dependence of NQR frequency and the spin-lattice relaxation rate 1/T_1 indicate that the crystal-electric-field splitting Δ_<CEF> between the ground state Γ_1 singlet and the first excited state Γ_4 triplet decreases with increasing pressure. The 1/T_1 below T_c=1.55K at P=1.91 GPa shows a power-law temperature variation and is proportional to T^5 at temperatures considerably below T_c, which indicates the existence of point nodes in the superconducting gap function. The data can be well fitted by the gap model Δ(θ)=Δ_0 sin θ with Δ_0=3.08k_BT_c. The relation between the superconductivity and the quadrupole fluctuations associated with the Γ_4 state is discussed.
社団法人日本物理学会の論文
2007-02-15