NMR evidence for the partially gapped state in ${\text{CeOs}}_2{\text{Al}}_{10}$

We report the results of a ${}^{27}\text{A}\text{l}$ nuclear magnetic resonance (NMR) study of ${\text{CeOs}}_2{\text{Al}}_{10}$ at temperatures between 4 and 300 K. This material has been of current interest due to indications of hybridization gap behavior below the transition temperature $T_o\simeq 29\text{K}$. Five ${}^{27}\text{A}\text{l}$ NMR resonance lines that are associated with five nonequivalent crystallographic aluminum sites have been resolved. For each individual aluminum site, the low-temperature NMR Knight shift goes over a thermally activated response. The temperature-dependent spin-lattice-relaxation rate exhibits a rapid drop below $T_o$, indicative of the formation of an energy gap in this material. We interpret the Knight shift and the relaxation-rate data in light of the presence of a pseudogap with residual electronic density of states at the Fermi level. Moreover, the magnitude of the pseudogap of 120 K is extracted from NMR results, in agreement with the value obtained from the inelastic neutron-scattering experiment.

Figure 1

(Color online) Room-temperature ${}^{27}\text{A}\text{l}$ NMR satellite lines for five nonequivalent crystallographic Al sites in ${\text{CeOs}}_2{\text{Al}}_{10}$.

Figure 2

(Color online) ${}^{27}\text{A}\text{l}$ NMR central transition spectra of ${\text{CeOs}}_2{\text{Al}}_{10}$ measured at various temperatures. The dashed vertical line denotes the position of the ${}^{27}\text{A}\text{l}$ reference frequency.

Figure 3

(Color online) Temperature dependence of observed ${}^{27}\text{A}\text{l}$ NMR Knight shifts in ${\text{CeOs}}_2{\text{Al}}_{10}$. Solid curves: fits to the thermally activated form described in the text.

Figure 4

(Color online) Variation in the observed Knight shifts versus the magnetic susceptibility in ${\text{CeOs}}_2{\text{Al}}_{10}$. Each solid line indicates the linear relationship. Inset: measured bulk magnetic susceptibility of ${\text{CeOs}}_2{\text{Al}}_{10}$ under a constant field of 1 T.

Figure 5

(Color online) Temperature dependence of ${}^{27}\text{A}\text{l}$ spin-lattice-relaxation rates in ${\text{CeOs}}_2{\text{Al}}_{10}$. The arrow indicates the phase transition temperature. The inset shows the low-$T$ relaxation rates which are fitted to the Korringa term plus activated behavior.