Manipulating spins in topological insulators

• Speaker: Dr. Joon Sue Lee (California NanoSystems Institute, UC, Santa Barbara)
• Date: Thursday, September 8, 2016, at 17:00
• Place: Jungho Seminar Room

In three-dimensional topological insulators, a band inversion by a strong spin-orbit coupling induces metallic surface states in the bulk band gap. The topological surface state is inherently spin-polarized and robust (“topologically protected”) against back scattering, which has attracted much attention from condensed matter physics and spintronics communities. Recently, it has been demonstrated that topological insulators are promising materials for spintronics: a spin-transfer torque of record efficiency was reported [1], and spin pumping measurements suggest a spin Hall angle of a topological insulator is larger than in many currently studied materials [2]. Current issues in “topological spintronics” include electrical detection and manipulation of the spin-polarized topological surface state. In this talk, I will discuss recent studies of direct electrical detection of the current-induced spin polarization in a topological insulator. Control of the resulting spin signals will be demonstrated by changing the direction of bias current and by tuning the chemical potential [3]. I will also discuss a different approach to manipulate the spin-textured surface state by breaking the time-reversal symmetry in a topological insulator interfaced with a ferromagnetic insulator. An opening of an energy gap is evidenced as the chemical potential approaches the Dirac point [4]. If time permits, I will briefly talk about another topic of my current studies: epitaxial-superconductor/two-dimensional semiconductor hybrid systems to investigate topological superconductivity towards quantum computing applications.

[1] A. Mellnik, J. S. Lee et al., Nature 511, 449 (2014)
[2] M. Jamali, J. S. Lee et al., Nano Lett., 15, 7126 (2015)
[3] J. S. Lee et al., Phys Rev B, 92, 155312 (2015)
[4] J. S. Lee et al., in preparation.