Heavy surface state in a possible topological Kondo insulator: Magnetothermoelectric transport on the (011) plane of ${\mathrm{SmB}}_6$

Motivated by the high sensitivity to Fermi surface topology and scattering mechanisms in magnetothermoelectric transport, we have measured the thermopower and Nernst effect on the (011) plane of the proposed topological Kondo insulator ${\mathrm{SmB}}_6$. These experiments, together with electrical resistivity and Hall effect measurements, suggest that the (011) plane also harbors a metallic surface with an effective mass on the order of ${10–10}^2$ $m_0$. The surface and bulk conductances are well distinguished in these measurements and are categorized into metallic and nondegenerate semiconducting regimes, respectively. Electronic correlations play an important role in enhancing scattering and also contribute to the heavy surface state.

Figure 1

XRD characterization of the ${\mathrm{SmB}}_6$ single crystal on (001) and (011) orientations. The inset shows a picture of an as-grown ${\mathrm{SmB}}_6$ single crystal with both (001) and (011) planes.

Figure 2

Electrical and thermoelectric transport properties of ${\mathrm{SmB}}_6$ on the (011) plane, plotted versus temperature. (a) The resistivity (${\rho }_{xx}$) and Hall coefficient ($R_H={\rho }_{yx}/B$, $B=9$ T). (b) The thermopower ($S_{xx}$) and Nernst coefficient (${\nu }_N=S_{xy}/B$, $B=9$ T). The solid lines in (a) are fits to the two-channel model discussed in the text. (c) and (d) respectively shows the field dependence of ${\rho }_{yx}$ and $S_{xy}$ at selected temperatures. The inset to (c) displays the Hall conductivity ${\sigma }_{xy}\left(B\right)$ at 0.3 K; while the inset to (d) is an Arrhenius plot of ${\rho }_{xx}\left(T\right)$, which shows thermal activation across a transport gap ${\Delta }_{bt}=40\left(2\right)$ K.

Figure 3

Temperature dependence of the thermopower $S_{xx}$ plotted against inverse temperature $1/T$. The inset displays the low-temperature variation of $S_{xx}\left(T\right)$.

Figure 4

The dimensionless ratio $\lambda =({\nu }_N/{\mu }_H)/(k_B/e)$ as a function of $T$. Also shown is the Hall mobility ${\mu }_H$. The inset is a schematic sketch of the band structure.