Spin-charge transport driven by magnetization dynamics on the disordered surface of doped topological insulators

Abstract

We theoretically study the spin and charge generation along with the electron transport on a disordered surface of a doped three-dimensional topological insulator/magnetic insulator junction by using Green's function techniques. We find that the spin and charge current are induced by not only local but also by nonlocal magnetization dynamics through nonmagnetic impurity scattering on the disordered surface of the doped topological insulator. We also clarify that the spin current as well as charge density are induced by spatially inhomogeneous magnetization dynamics, and the spin current diffusively propagates on the disordered surface. Using these results, we discuss both local and nonlocal spin torques before and after the spin and spin current generation on the surface, and provide a procedure to detect the spin current.

Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

“…Spin-charge conversion processes in topologicalinsulator/FM bilayers have been studied by several authors (Fujimoto and Kohno, 2014;Linder, 2014;Sakai and Kohno, 2014;Taguchi et al, 2015;Tserkovnyak et al, 2015). The low energy Hamiltonian readsĤ = vσ • (p × z) + ∆ 2σ • m, where the first term models the Dirac cone and the second term is the exchange.…”

Spin-orbit torque in two-dimensional antiferromagnetic topological insulators

“…Recently, three-dimensional TI have been used to achieve large SOT in an adjacent ferromagnet [27][28][29][30]. In spite of significant theoretical efforts to model the SOT exerted on homogeneous ferromagnets [37,[40][41][42][43][44][45][46] and magnetic textures [47][48][49][50][51][52], the exact nature of the torque observed experimentally remains a matter of debate as it is not clear whether surface states are still present and how bulk and surface transport contribute to the different components of the torque. Besides significant challenges in terms of materials growth, the main difficulty lies in the fact that magnetism itself breaks the topological protection of surface states [53][54][55][56][57][58], which prevents us from taking full advantage of the gigantic spin-orbit coupling of * sumit.ghosh@kaust.edu.sa † aurelien.manchon@kaust.edu.sa the Dirac cones.…”

Dirac spin-orbit torques and charge pumping at the surface of topological insulators

“…These two effects are related to each other via the Onsager reciprocity relation and can be treated on equal footing. The spin-to-charge conversion process has been investigated experimentally in ferromagnet/topological insulator heterostructures [22][23][24][25] (e.g., FM/Bi 2 Se 3 ), and some of its aspects have been treated theoretically [47,48].…”

“…Various phenomena such as the topological magnetoelectric effect [30,31], STT and current-driven magnetization dynamics [32][33][34][35][36][37], the interplay between spin and charge [38][39][40][41][42], and spin transport in magnetic TIs [43][44][45][46][47][48] have been studied theoretically. Despite these important theoretical efforts, major puzzles remain to be understood such as the emergence of gigantic dampinglike torque [19,20], the sizable angular dependence of the SOT [20], and the significant discrepancies between the spin-charge conversion rates reported in the SOT experiments [19,20,26,27] and the spin-pumping experiments [22][23][24][25].…”