Abstract
This work experimentally investigated quantum transport characteristics of heavily doped bismuth selenide topological insulator nanoribbons to understand their physical origins. Transport properties of nanoribbons were measured via a suspended micro-device for eliminating the substrate effect. A series of quantum transport behaviors such as weak antilocalization, Shubnikov-de Haas oscillations, universal conductance fluctuation, and linear perpendicular-field magnetoresistance have been systematically studied to achieve a coherent understanding on their origins in topologically protected surface states, band bending, or bulk states. The parallel-field magnetoresistance, however, is found to be diverse, which can exhibit negative or positive values for the whole measurement range of the magnetic field strength or change from positive to negative values with the increase of the magnetic field strength. The tunable behavior of the parallel-field magnetoresistance is suggested to be the collective effects of the positive magnetoresistance from surface transport and the negative magnetoresistance possibly owing to the axial anomaly, resulting from long-range ionic impurity-scattering processes in bulk carriers.
Highlights
As a new quantum state of matter, the three-dimensional (3D)topological insulators (TIs) are fully gapped in the bulk but exhibit an odd number of massless Dirac cones on the surface, originating from the strong spin-orbit interaction that causes a band inversion.[1]
Topological insulators (TIs) are fully gapped in the bulk but exhibit an odd number of massless Dirac cones on the surface, originating from the strong spin-orbit interaction that causes a band inversion.[1]. Electrons in these topological surface states (TSSs) have a helical spin structure in momentum space that is protected by time-reversal symmetry (TRS), which can be applied in spintronics and quantum computing.[2,3]
Some signatures of two-dimensional (2D) surface transport have already been observed such as Shubnikov-de Haas oscillations (SdHOs),[6,7] weak antilocalization (WAL),[8,9] nonsaturating linear magnetoresistance (LMR),[10,11] and universal conductance fluctuation (UCF).[12,13]
Summary
Topological insulators (TIs) are fully gapped in the bulk but exhibit an odd number of massless Dirac cones on the surface, originating from the strong spin-orbit interaction that causes a band inversion.[1]. Some signatures of two-dimensional (2D) surface transport have already been observed such as Shubnikov-de Haas oscillations (SdHOs),[6,7] weak antilocalization (WAL),[8,9] nonsaturating linear magnetoresistance (LMR),[10,11] and universal conductance fluctuation (UCF).[12,13] the quantum signals of electron transport of TSSs are often obscured by electron transport in parallel conduction channels including both the bulk and the 2D electron gas (2DEG) formed near the surface owing to bending of bulk bands Both the bulk transport and the 2DEG transport complicate the observed phenomena and lead to the widely varying data in the literature, resulting in controversial and conflicting analyses and interpretations.[15,18,19,20] Few researchers have systematically studied and discussed multiple quantum signatures in one material system. This tunable parallel-field MR is considered to be the collective effects of a positive MR from surface transport and a negative MR possibly from bulk transport due to ionic impurity scattering
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