Features of Longitudinal Magnetoresistance and Shubnikov de Haas Oscillations in Bi_1-xSb_x Semiconductor Nanowires

CZU 537.9, 53.06, 53.043

DOI  https://doi.org/10.5281/zenodo.4305606

The features of the manifestation of the properties of topological insulators (TIs) and quantum size effects on the longitudinal magneto-resistance (LM) (H||I) of Bi-17at%Sb single-crystal semiconductor wires prepared by liquid phase casting (Ulitovsky method) having orientation along the axis and diameters of 75–1000 nm have been studied. At high temperatures (T > 50 K), the quantum size effect was evident as an increase in the energy gap of DE ~ d^-1 of Bi-17at%Sb semiconductor wires, with a decrease in wire diameter d. A decrease in temperature (T < 50 K) leads to a transition from the semiconductor dependence R(T) to the metallic dependence, with a decrease in the wire diameter d; the transition indicates the presence of the surface states characteristic of TIs. In a diameter range of 200–350 nm, on the LM (H II I) in weak magnetic fields (H < 3 T), the Shubnikov de Haas (SdH) oscillations are observed; they are used to calculate the Dingle temperature, cyclotron masses, carrier mean free path, and charge carrier mobilities m = 11´10³ cm²/sec. On the LM of Bi-17at%Sb wires at 4.2 K, a singularity in the form phase shift of the Landau levels index on the SdH oscillations of an anomalous maximum in the thickness dependence of the LM at 4.2 K is observed; it is associated with the semiconductor-metal transition due to a significant contribution of the surface states of the TI with a decrease in the wire diameter d. Taken together, the singularities on the LM, the phase shift of the SdH oscillations, high mobility and anisotropy of charge carriers, and an increase in conductivity with a decrease in the wire diameter d indicate the presence of surface states in thin semiconductor Bi_1-xSb_x wires with a Fermi energy of the “Dirac cone” type, which are highly sensitive to the wire diameter, temperature, and the magnitude and direction of the magnetic field and lead to new features of the transport properties of TIs in low-dimensional structures.

Keywords: single-crystal nanowires, topological insulator, quantum oscillations, longitudinal magneto-resistance, surface state, quantum size effect.