Influence of helical spin structure on the magnetoresistance of an ideal topological insulator

Abstract

In an ideal topological insulator, the helical spin structure of surface electrons suppresses backscattering and thus can enhance surface conductivity. In this study, we investigate the effect of perpendicular magnetic field on the spin structure of electrons at the Fermi energy and define a magnetic-field dependent topological enhancement factor using Boltzmann transport and calculate this factor for different disorder potentials, ranging from short-range disorder to screened Coulomb potential. Within the Boltzmann approximation, the topological enhancement factor reaches its maximum value of 4 for a short-range disorder at zero magnetic field and approaches a value of 1 at high magnetic fields. The topological enhancement factor becomes independent of the nature of the disorder potential at high magnetic fields.

Ultrafast manipulation of topologically enhanced surface transport driven by mid-infrared and terahertz pulses in Bi2Se3

“…Most intriguingly, we show that the topological enhancement of surface transport suppresses the surface electron scattering rate as compared to the bulk, i.e., γ BS /γ SS ∼3.80 in equilibrium. This result is consistent with surface helical spin transport in the presence of short-range disorder [27]. The distinct spectral-temporal characteristics observed here are absent for elevated lattice temperature, high pump photon frequency and high fluence.…”

“…We show that the topological enhancement of surface transport suppresses the surface electron scattering rate as compared to the bulk, i.e., γ BS / γ SS ~3.80 in equilibrium. This result is consistent with surface helical spin transport in the presence of short-range disorder 31 . Moreover, the clear similarities between mid-IR and THz pumping and their distinct difference from high-photon-energy cases clearly show: (1) ultrafast manipulation of the surface and bulk THz conductivities via wavelength-selective pumping; (2) intraband vs. interband excitation mechanisms driven by low and high-photon-energy pumping.…”

“…Remarkably, this value matches very well with the topological enhancement factor, 4, for protected, helical spin transport of non-interacting fermions in the presence of short-range disorder such as structural defects and surface or interface roughness. In the presence of long range, Coulomb disorder, this enhancement decreases from 4 to 2 due to increase of screening 31 . Furthermore, as shown in Fig.…”

Comprehensive surface magnetotransport study of SmB6

“…We note that although the surface of a 3D TI prohibits back scattering, this does not guarantee a high mobility. Absence of back scattering only results in a mild correction to the scattering time compared to the case where back scattering is allowed 37 . In the case of a exposed surfaces, the carriers are expected to scatter strongly from disorder arising from the non-epitaxial native oxide that must be present on all SmB 6 transport samples.…”

Thermoelectric Properties of Topological Insulators

“…Comparison of the obtained results gives the ratio τ / τ 2D = 4, i.e., when carriers are scattered by point defects, the transport relaxation time of Dirac fermions at the Fermi level exceeds the value of the corresponding parameter of an ordinary two‐dimensional electron gas by four times. Different comparative analysis of the effectiveness of topological protection gives similar result for the ratio of the relaxation times τ / τ 2D of electron scattering by ionized impurities and point defects.…”