Spin-dependent scattering induced negative magnetoresistance in topological insulator Bi2Te3 nanowires

Biplab Bhattacharyya,S Auluck,R P Aloysius,Chenliang Su,Bahadur Singh,Anurag Gupta,T D Senguttuvan,Sudhir Husale,Hsin Lin,Reena Yadav

doi:10.1038/s41598-019-44265-5

Abstract

Studies of negative magnetoresistance in novel materials have recently been in the forefront of spintronic research. Here, we report an experimental observation of the temperature dependent negative magnetoresistance in Bi2Te3 topological insulator (TI) nanowires at ultralow temperatures (20 mK). We find a crossover from negative to positive magnetoresistance while increasing temperature under longitudinal magnetic field. We observe a large negative magnetoresistance which reaches −22% at 8 T. The interplay between negative and positive magnetoresistance can be understood in terms of the competition between dephasing and spin-orbit scattering time scales. Based on the first-principles calculations within a density functional theory framework, we demonstrate that disorder (substitutional) by Ga+ ion milling process, which is used to fabricate nanowires, induces local magnetic moments in Bi2Te3 crystal that can lead to spin-dependent scattering of surface and bulk electrons. These experimental findings show a significant advance in the nanoscale spintronics applications based on longitudinal magnetoresistance in TIs. Our experimental results of large negative longitudinal magnetoresistance in 3D TIs further indicate that axial anomaly is a universal phenomenon in generic 3D metals.

Highlights

Over the last decade, numerous theoretical and experimental studies on topological states of quantum matter have revolutionized research in condensed matter physics
It is well known that conductivity corrections resulting from the quantum interference of time-reversed closed loops around an impurity or scattering point give rise to weak localization (WL) or weak antilocalization (WAL) effects, which can be directly observed through MR measurements[8,9,10]
In topological insulator (TI), WAL effect is expected to manifest as a cusp-like feature in the MR curve at zero magnetic (B) field due to the presence of strong spin-momentum locking of the metallic topological surface states (TSSs) that leads to a π-Berry phase and suppresses backscattering[2,8]

Summary

Introduction

Numerous theoretical and experimental studies on topological states of quantum matter have revolutionized research in condensed matter physics. Several NMR observations have been reported in TIs under both perpendicular and parallel B-fields, for example, in ultrathin Bi2Se3 films due to crossover between WL and WAL of bulk electrons[23], in ultrathin (BixSb1−x)2Te3 films due to opening of energy gap in TSS that modifies the Berry phase and leads to competing WL and WAL at low B-fields[24], in ultrathin (Bi1−xSbx)2Te3 films due to disorder-induced Anderson localization[25], in Sn-doped Bi2Te3 polycrystalline films[13] and Bi2(Te0.4Se0.6)[3] film[26] due to WL effect of bulk states, in Bi2Se3 nanoribbons due to Zeeman energy induced surface Dirac cone deformation and spin-dependent scattering of TSS27, in BiSbTeSe2 nanoflakes due to disorder induced enhancement of defect states density from Ar+ ion milling[28], in TlBi0.15Sb0.85Te2 due to formation of charge puddles in disordered bulk[29], in epitaxial Bi2Se3 thin films due to underlying scattering mechanism[21] and in Bi2Se3−ySy due to non-trivial bulk conduction and appearance of electron puddles from sulphur doping[30]. Qualitative analysis of the effect of orientation of B-field, excitation current and spin-polarization of the TSS along-with the bulk conductance interference can explain the origin of NMR and other MR characteristics observed in all the devices via spin-dependent scattering mechanism of surface and bulk electrons on local magnetic moments

Methods

Results

Conclusion