Abstract:
The magnetoresistivities $\rho_{22}(H)$ and $\rho_{32}(H)$ and the Hall coefficient $R_{32.1}$ for single-crystal samples of the $n$-Bi$_{0.93}$Sb$_{0.07}$ semiconducting alloy have been measured at low temperatures in magnetic fields up to $H$ = 14 T at $H\parallel C_2$. The samples with three electron concentrations $n_1$ = 1.25 $\times$ 10$^{16}$ cm$^{-3}$, $n_2$ = 3.5 $\times$ 10$^{16}$ cm$^{-3}$, $n_3$ = 1.6 $\times$ 10$^{17}$ cm$^{-3}$ have been studied. The strong anisotropy of the electron spectrum of the alloys has made it possible to observe quantum oscillations of the magnetoresistivity $\rho_{22}(H)$ at $H\parallel C_2$ for electrons of the secondary ellipsoids with the transition to the quantum limit in high magnetic fields. However, in the same magnetic fields, the quantization condition for electrons of the main ellipsoid is not satisfied. An increase in the energy of electrons of the secondary ellipsoids in the magnetic fields of the quantum limit leads to their migration to the main ellipsoid. After the complete migration, the Fermi energy for the alloy samples with the electron concentrations $n_1$, $n_2$, and $n_3$ increases from 7.0 to 11.3 meV, from 11.0 to 17.1 meV, and from 20.2 to 30.6 meV, respectively. After the migration, the magnetoresistivity for electrons of the main ellipsoid increases with an increase in the magnetic field and the specific features in the behavior of the kinetic coefficients are observed in the vicinity of the magnetic field $H$ = 10 T. Therefore, the electronic topological transition from the three-valley electron spectrum to the single-valley electron spectrum occurs in the Bi$_{0.93}$Sb$_{0.07}$ single crystals for $H\parallel C_2$ at low temperatures in the range of magnetic fields of the quantum limit.
