S123b-NQR study of unconventional superconductivity in the filled skutterudite heavy-fermion compound PrOs4Sb12 under high pressure up to 3.82 GPa

Abstract

We report S123b nuclear-quadrupole-resonance (NQR) measurements of the filled skutterudite heavy-fermion superconductor PrOs4Sb12 under high pressure. The temperature dependence of NQR frequency and the spin-lattice relaxation rate 1/T1 indicate that the crystal-electric-field splitting ΔCEF between the ground-state Γ1 singlet and the first-excited-state Γ4(2) triplet decreases with increasing pressure. ac-susceptibility measurements indicate that the superconducting transition temperature (Tc) also decreases with increasing pressure. However, above P∼2 GPa, both ΔCEF and Tc do not depend on external pressure up to P=3.82 GPa. These pressure dependences of ΔCEF and Tc suggest an intimate relationship between quadrupole excitations associated with the Γ4(2) level and unconventional superconductivity in PrOs4Sb12. In the superconducting state, 1/T1 below Tc=1.55 and 1.57 K at P=1.91 and 2.63 GPa shows a power-law temperature variations and is proportional to T5 at temperatures considerably below Tc. These data can be well fitted by the gap model Δ(θ)=Δ0 sin θ, with Δ0=3.08kBTc and 3.04kBTc for P=1.91 and 2.63 GPa, respectively. The results indicate that there exist point nodes in the gap function.

Source-reported materials — not catalogue approval

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