November 9, 2022
Spin Dynamics and Topological Spin transport in low-symmetry transition metal dichalcogenide monolayers
Nonlocal transport in mesoscopic devices provides unique fingerprints of the underlying processes taking place. Quantization plateaus of quantum spin Hall phases, detection of the spin Hall effect, or measurement of spin relaxation in nonmagnetic materials are only a few examples where nonlocal transport schemes are employed. In this talk, I will show how quantum transport within the Landauer-Büttiker formalism can be used to study spin transport in nonlocal multi-terminal devices [1] as well as to detect topological phases.
Firstly, I will theoretically show unconventional forms of the spin Hall effect and the quantum spin Hall effect in monolayers of MoTe2 and WTe2. Due to the low crystal symmetry, the spin polarization of electrons in these TMDs displays a momentum invariant (persistent) spin texture fixed in a direction along the yz plane, and as a result, the spin transport displays anisotropic spin relaxation. Furthermore, the spin Hall effect exhibits an unconventional component, with spin accumulation generated in the plane, which together with the conventional out-of-plane polarization, forms an oblique or canted spin Hall effect. Remarkably, the efficiency of both spin transport and spin generation is predicted to be exceptionally large [2]. The symmetry constraints underlying these phenomena also extend to the nontrivial topological phase appearing when the Fermi level is placed in the band gap, resulting in a novel canted quantum spin Hall effect [3]. The corresponding topologically protected edge states are robust to disorder and carry spins polarized in the same canted direction as the persistent spin texture found at the bottom of the conduction bands.
Marc Vila Tusell is a postdoc at the Lawrence Berkeley National Laboratory and the department of physics of the University of California, Berkeley, working with Professor Joel Moore. He completed his bachelor's in Nanoscience and Nanotechnology from the Autonomous University of Barcelona and obtained his Ph.D. in theoretical physics from the same university in 2020. His Ph.D. research, carried out at the Catalan Institute of Nanoscience and Nanotechnology, focused on the theoretical exploration of spin transport in two-dimensional quantum materials such as graphene, transition metal dichalcogenides, and topological insulators. Currently, he is interested in transport properties of magnetic materials and spin-orbitronics, i.e. the usage of spin-orbit coupling to envision spintronic applications and topological states of matter.