Chapter 12 - Magnetically Doped Topological Insulator Thin Films

Abstract

Topological insulators (TIs) are a recently discovered class of materials characterized by massless spin-helical Dirac surface states with time-reversal symmetry (TRS) at the interface of non-topological insulating materials. The backscattering of surface carriers in TIs is suppressed as the spin and momentum direction are locked and the nonmagnetic impurities in TIs can change only the direction of momentum but not spin. The massless surface states of TIs have potential applications in low dissipation spintronics devices. The TRS protecting the surface state of TIs against backscattering can be broken by introducing magnetic impurities. The surface carriers of magnetically doped TI materials, below the magnetic ordering temperature, can acquire an effective mass and a surface energy gap opening. Synthesis of thin film and nano-structured TIs is important to maximize the surface/bulk ratio and highlight the surface contribution. Moreover, exploration of magnetic element that can be incorporated into TI crystals while maintaining crystal quality is also critical to understand ferromagnetic ordering in TIs. Many important phenomena, such as anomalous quantum Hall effect, Majorana fermion, magnetoelectric effect proposed to exist within TIs require nontrivial energy band structure, that are the induced surface gap are within the bulk bandgap and the Fermi level is within both gaps. This chapter will introduce properties of TIs, synthesis of nanoscale TI thin films, and the potential application of magnetically doped TIs.