Novel Phase Transition Near the Quantum Critical Point in the Filled-Skutterudite Compound CeOs4Sb12: an Sb-NQR Study

Abstract

We report on a novel phase transition at $T$ = 0.9 K in the Ce-based filled-skutterudite compound CeOs${}_4$Sb${}_{12}$ via measurements of the nuclear-spin lattice relaxation rate $1/T_1$ and nuclear quadrupole resonance (NQR) spectrum of Sb nuclei. The temperature ($T$) dependence of $1/T_1$ behaves as if approaching closely an antiferromagnetic (AFM) quantum critical point (QCP), following the relation $1/T_1\propto T/(T-T_{\mathrm{N}}{)}^{1/2}$ with $T_{\mathrm{N}}=0.06$ K in the range of $T=1.3-25$ K. The onset of either the spin-density-wave (SDW) or charge-density-wave (CDW) order at $T_0=0.9$ K, that is, of the first order, is evidenced by a broadening of the NQR spectrum and a marked reduction in $1/T_1$ just below $T_0$. The $f$-electron-derived correlated band realized in CeOs${}_4$Sb${}_{12}$ is demonstrated to give rise to the novel phase transition on the verge of AFM QCP.

4pages, 5figures