Surface States Transport in Topological Insulator $\mathrm{Bi}_{0.83}\mathrm{Sb}_{0.17}$ Nanowires

Abstract

We investigate the transport properties of topological insulator (TI) $\mathrm {Bi}_{0.83}\mathrm {Sb}_{0.17}$ nanowires. Single-crystal nanowire samples with diameters ranging from 75 nm to 1.1 $\mu$m are prepared using high frequency liquid phase casting in a glass capillary; cylindrical single crystals with (10$\bar{1}$1) orientation along the wire axis are produced. $\mathrm {Bi}_{0.83}\mathrm {Sb}_{0.17}$ is a narrow-gap semiconductor with an energy gap at the L point of the Brillouin zone, $\Delta E = 21$ meV. The resistance of the samples increases with decreasing temperature, but a decrease in resistance is observed at low temperatures. This effect is a clear manifestation of TI properties (i.e., the presence of a highly conducting zone on the TI surface). When the diameter of the nanowire decreases, the energy gap $\Delta E$ grows as 1 / d (for diameter $d = 1.1 \upmu$m and $d =75$ nm $\Delta E = 21$ and 45 meV, respectively), which proves the presence of the quantum size effect in these samples. We investigate the magnetoresistance of $\mathrm {Bi}_{0.83}\mathrm {Sb}_{0.17}$ nanowires at various magnetic field orientations. Shubnikov-de Haas oscillations are observed in $\mathrm {Bi}_{0.83}\mathrm {Sb}_{0.17}$ nanowires at $T = 1.5$ K, demonstrating the existence of high mobility ($\upmu _S = 26{,}700--47{,}000$ $\mathrm {cm^2V^{-1}s^{-1}}$) two-dimensional (2D) carriers in the surface areas of the nanowires, which are nearly perpendicular to the $C_3$ axis. From the linear dependence of the nanowire conductance on nanowire diameter at $T = 4.2$ K, the square resistance $R_\mathrm{sq}$ of the surface states of the nanowires is obtained ($R_\mathrm{sq} =70$ Ohm).