Anistropy of the Constant-Energy Surfaces inn-Type BiTe32andBi2Se3from Galvanomagnetic Coefficients

Abstract

Low-field galvanomagnetic coefficients have been measured on single crystals of ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ and ${\mathrm{Bi}}_{2}$${\mathrm{Se}}_{3}$ at 76 \ifmmode^\circ\else\textdegree\fi{}K in fields to 9 kG. Using a six-valley ellipsoid model in the isotropic relaxation-time approximation, the mass parameters of the ellipsoids are calculated for both compounds. The discrepancy between previously reported galvanomagnetic data and de Haas-van Alphen data for ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ can be minimized by recalculating the mass parameters from the galvanomagnetic data and by not assuming complete degeneracy. The experimental data on ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ are in agreement with those reported earlier. There is also very good evidence of second-band effects at high electron concentrations (> ${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$), as has been previously suggested. The constant-energy surfaces undergo an apparent change in shape between low- and high-concentration samples. Data on ${\mathrm{Bi}}_{2}$${\mathrm{Se}}_{3}$ indicate that the constant-energy surfaces are more spherical than in the case of ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$.