Temperature evolution of transverse magnetoresistance due to forming the topological insulator state in single-crystalline n-type Bi2Te2.7Se0.3

Abstract

Specific features in magnetotransport properties due to gradual forming the topological insulator state in sample of single-crystalline n-type Bi2Te2.7Se0.3 during its cooling were analyzed. The electrical resistivity of sample, measured from 2 K to 240 K, corresponds to partially degenerate semiconductor and dominantly depends on T-effect on electron mobility. The moblity is governed by electron–phonon scattering above T C = 50 K, whereas below T C electron–electron scattering is dominant scattering mechanism. With increasing temperature, electron content linearly increases above T C , whereas below T C electron content is very weakly T-dependent. Transverse magnetoresistance of sample is positive and strongly T-dependent. Two features, which are characteristic for topological insulators, were found in the magnetoresistance. First feature is a crossover from quadratic to linear magnetoresistance, observed within T C < T < 240 K range. Crossover field B C decreases with decreasing temperature. Linear magnetoresistace is quantum one that can be due to presence of Dirac fermions, which occupy the lowest Landau level under magnetic field. Second feature is another crossover from combined quadratic-linear to dip-shaped magnetoresistrance, observed at T ≤ T C . Dip-shaped magnetoresistrance is related to weak antilocalization (WAL) phenomenon. The WAL phenomenon and the electron–electron scattering process coexist at the same temperature range. Dip-shaped magnetoresistrance was analysed by in frames of the Hikami-Larkin-Nagaoka model, developed for systems with strong spin–orbit coupling. At cooling below ∼ 30 K, the effective dephasing length rapidly increases that is dominantly related to the electron–electron scattering process, too. The parameter α, characterizing the number of conduction channels, contributing to electron transport, is close to 0.5. This value α corresponds to a single topologically non-trivial conduction channel.