Seminar – Topological Spin Transport in Quantum Materials and Entanglement

On Monday May 13, 2024 at 14:00 we have the pleasure to welcome Prof. Stephan ROCHE (ICREA, Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC, BIST). He will give us a seminar entitled :

Topological Spin Transport in Quantum Materials and Entanglement

Place: IRIG/SPINTEC, CEA Building 10.05, auditorium 445 (access needs authorization request it before May 7th to

Video conference:
Meeting ID: 987 6986 7024 Passcode: 025918

Abstract: I will discuss spin transport properties in two-dimensional materials, topological insulators and van der Waals heterostructures by first presenting the frame of efficient linear scaling spin transport methodologies which enable the simulation of realistic (three-dimensional) models of topological matter including the presence of disorder. We will then review the initial claims of giant spin Hall effect in graphene-based devices and the upper limit that could be achieved by proximitized graphene with strong spin-orbit coupling materials [1].

Next, I will present theoretical spin transport features in MoTe2 and WTe2-based materials which are particularly interesting Quantum Materials [2]. By focusing on the monolayer limit, using DFT-derived tight-binding models and using both efficient bulk and multi-terminal formalisms and techniques [3,4], I will show the emergence of new forms of intrinsic spin Hall effect (SHE) that produce large and robust in-plane spin polarizations. Quantum transport calculations on realistic device geometries with disorder demonstrate large charge-to-spin interconversion efficiency with gate tunable spin Hall angle as large as θxy≈80%, and SHE figure of merit λs.θxy∼8-10 nm, largely superior to any known SHE material [5]. I will show our theoretical prediction of an unconventional canted quantum spin Hall phase in the monolayer Td-WTe2, which exhibits hitherto unknown features in other topological materials [6]. The low symmetry of the structure induces a canted spin texture in the yz plane, dictating the spin polarization of topologically protected boundary states. Additionally, the spin Hall conductivity gets quantized (2e2/h) with a spin quantization axis parallel to the canting direction. We also predict the control of the canted QSHE by electric field [7]. I will finally discuss the role of entanglement between intraparticle degrees of freedom in spin transport and dynamical patterns of entanglement, as enabling novel platform for generating and manipulating quantum entanglement between internal and interparticle degrees of freedom [8].

[1] J. F. Sierra, J. Fabian, R. K. Kawakami, S. Roche, S. O. Valenzuela, “Van der Waals heterostructures for spintronics and opto-spintronics”, Nature Nanotechnology 16 (8), 856-868 (2021)
[2] F. Giustino et al. The 2020 Quantum Materials Roadmap, J. Phys. Mater. 3 042006 (2020)
[3] M. Vila et al. “Nonlocal Spin Dynamics in the Crossover from Diffusive to Ballistic Transport”, Physical Review Letters 124, 196602 (2020)
[4] Z. Fan et al. “Linear scaling quantum transport methodologies”, Physics Reports 903, 1-69 (2021)
[5] M. Vila, C.H. Hsu, J.H. Garcia, L.A. Benítez, X. Waintal, S. Valenzuela, V. Pereira, S. Roche, “Charge-to-Spin Interconversion in Low-Symmetry Topological Materials”, Physical Review Research 3, 043230 (2021)
[6] J. H. Garcia, M. Vila, C.H. Hsu, X. Waintal, V.M. Pereira, S. Roche, “Canted Persistent Spin Texture and Quantum Spin Hall Effect in WTe2″, Physical Review Letters 125 (25), 256603 (2020)
[7] J. H. Garcia, J. You, et al. S. Roche, “ Electrical control of spin-polarized topological currents in monolayer Physical Review B 106 (16), L161410 (2022)
[8] B. G. de Moraes, A. W. Cummings, S. Roche, “Emergence of intraparticle entanglement and time-varying violation of Bell’s inequality in Dirac matter”, Physical Review B 102 (4), 041403 (2020); J. Martinez, A.W. Cummings and S. Roche arXiv preprint arXiv:2310.17950

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