Magnetoresistance from broken spin helicity (1412.4065v1)

Abstract: The propensity of some materials and multilayers to have a magnetic field dependent resistance, called magnetoresistance, has found commercial applications such as giant magnetoresistance harddisk read heads. But magnetoresistance can also be a powerful probe of electronic and magnetic interactions in matter. For example, magnetoresistance can be used to analyze multiband conductivity, conduction inhomogeneity, localized magnetic moments, and (fractional) Landau level structure. For materials with strong spin-orbit interaction, magnetoresistance can be used as a probe for weak antilocalization or a nontrivial Berry phase, such as in topological insulator surface states. For the three dimensional topological insulators a large and linear magnetoresistance is often used as indication for underlying non-trivial topology, although the origin of this effect has not yet been established. Here, we observe a large magnetoresistance in the conducting bulk state of Bi$_2$Te$_3$. We show that this type of large magnetoresistance is due to the competition between helical spin-momentum locking (i.e. spin rotates with momentum direction) and the unidirectional spin alignment by an applied magnetic field. Warping effects are found to provide the (quasi) linear dependence on magnetic field. We provide a quantitative model for the helicity breaking induced magnetoresistance that can be applied to a vast range of materials, surfaces or interfaces with weak to strong spin-orbit interactions, such as the contemporary oxide interfaces, bulk Rashba systems, and topological insulator surface states.