Angle-controlled \(\mathrm {^{11}}\)B-NMR studies of Kondo insulator SmB\(_{6}\)

In SmB \(_6\) ${}_6$ , the prototypical material of valence fluctuations and Kondo semiconductors, there remain several unsolved problems in the bulk properties at low temperatures. We have studied a single crystalline sample of SmB \({_6}\) ${}_6$ by \(^{11}\) ${}^{11}$ B-nuclear magnetic resonance (NMR) measurements with the precise control of the field direction in the \(\left( \bar{1} 1 0 \right) \) $\left(\overline{1},10\right)$ plane. The temperature dependence of the nuclear quadrupole frequency \(\nu _\textrm{Q}\) ${\nu }_{\text{Q}}$ and the full width at half maximum (FWHM), estimated from obtained spectra indicates that there are two distinct low-temperature regions in SmB \(_6\) ${}_6$ : the first is the region down to approximately 10 K, where a decrease in the FWHM and an increase in \(\nu _\textrm{Q}\) ${\nu }_{\text{Q}}$ with lowering temperature are understood in the framework of the evolution of the hybridization effects between 4f and conduction electrons accompanied with an intermediate valence state. Below 10 K, the second region, \(\nu _\textrm{Q}\) ${\nu }_{\text{Q}}$ and the FWHM undergo a sharp change in their temperature dependence. Through both electrical and magnetic interactions, the present results suggest that the low-temperature state below 10 K is dominated by additional physical properties other than the hybridization and the valence fluctuations.