![]() ![]() We find a strong angle-independent WAL contribution in Bi 2Se 3 resulting from 3D bulk states. We observe the 2D weak anti-localization (WAL) indicative of topological materials and we explore anisotropic magnetoresistance effects. In this work, we perform magnetoresistance (MR) measurements on four Bi-based topological material films: Bi 2Se 3, Bi 2Te 3, and two films with a mixture of Se and Te under constant growth conditions. Moreover, in order to use these materials in the proposed applications, the material properties must be optimized. The interest, therefore, is to obtain high quality epitaxial thin films that facilitate transport mediated by topological surface states distinct from bulk electronic states. Specifically, the Bi 2Te 2Se alloy represents a special line compound whose bulk conductivity is sufficiently low that surface and bulk transport may be distinguished 25. Further rationale for investigating Bi 2Te xSe 3−x alloys is that they offer robust Dirac dispersion for surface conduction combined with a path toward reduced bulk conductivity compared to their parent compounds at either x = 0 or 3 24. Insight into the nature of the conducting surface states as well as their robustness to chemical substitution is vital to effectively utilizing these materials. Despite the great amount of research into their topological nature, little work has been done to understand how changing concentrations with either Se or Te affect the overall topological properties. This is because they are relatively simple to grow as thin films 20, 21, 22, and both possess a single Dirac point at accessible doping levels 23. In particular, devices for applications in advanced computing and logic beyond Moore’s law have been envisioned 9, 10, 11, 12, 13.īi 2Se 3 and Bi 2Te 3 are prototypical TIs that have been widely studied in order to understand this vibrant class of materials 14, 15, 16, 17, 18, 19. These surface states have a variety of potential applications owing to their robustness resulting from topological protection, potentially high mobilities, and spin-momentum locking, making them ideal candidates for spin-transport 3, 4, 5, 6, 7, 8. The extremely large magnetoresistance and high mobility of topological insulators have great technological value and can be exploited in magneto-electric sensors and memory devices.In topological insulators (TIs), a finite band gap in the bulk is accompanied by metallic surface states with linear dispersion, resulting from band inversion 1, 2. At high charge carrier concentrations, there is a greater number of conduction channels and a decrease in the phase coherence length compared to low charge carrier concentrations. The physical parameters characterizing the WAL effects are calculated using the Hikami-Larkin-Nagaoka formula. The observations of an extremely large, non-saturating magnetoresistance, more » and ultrahigh mobility in the samples with lower carrier density further support the presence of surface states. WAL due to topological surface states shows no dependence on the nature (electrons or holes) of the bulk charge carriers. At high charge carrier density the WAL curves scale with neither the applied field nor its normal component, implying a mixture of bulk and surface conduction. At low charge carrier density the WAL curves scale with the normal component of the magnetic field, demonstrating the dominance of topological surface states in magnetoconductivity. Here, weak antilocalization (WAL) effects in Bi 2Te 3 single crystals have been investigated at high and low bulk charge carrier concentrations. This anisotropy can be used in anisotropic magnetic sensor applications. Finally, the anisotropy in magnetoresistance with respect to angle has been described by the Hikami-Larkin-Nagaoka theory. The estimated Zeeman g-factor and the strength of Coulomb screening parameter agree well with the theory. The parallel field data have been explained using both the contributions from the Maekawa-Fukuyama localization theory for non-interacting electrons and Lee-Ramakrishnan theory of electron-electron interactions. For parallel field magnetoresistance, more » we have confirmed the presence of Zeeman effect which is otherwise suppressed in perpendicular field magnetoresistance due to strong spin-orbit coupling. The estimation of these charge and spin transport parameters are useful for spintronics applications. We have obtained the out-of-plane spin-orbit relaxation time to be small and the in-plane spin-orbit relaxation time to be comparable to the momentum relaxation time. The perpendicular field magnetoresistance has been explained by the Hikami-Larkin-Nagaoka theory alone in a system with strong spin-orbit coupling, from which we have estimated the mean free path, the phase coherence length, and the spin-orbit relaxation time. = thin film with field up to 9 T over 2–20 K temperatures. ![]()
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