Staff directory
Jose Hugo García Aguilar
Team Leader
josehugo.garcia(ELIMINAR)@icn2.cat
Theoretical and Computational Nanoscience
- ORCID: 0000-0002-5752-4759
Publications
2024
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Emerging Spin-Orbit Torques in Low-Dimensional Dirac Materials
Joaquín Medina Dueñas; José H. García; Stephan Roche Physical Review Letters; 132 (26) 2024. 10.1103/physrevlett.132.266301. IF: 8.100
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Field-Free Spin-Orbit Torque Switching in Janus Chromium Dichalcogenides
Vojacek, Libor; Duenas, Joaquin Medina; Li, Jing; Ibrahim, Fatima; Manchon, Aurelien; Roche, Stephan; Chshiev, Mairbek; Garcia, Jose H Nano Letters; 2024. 10.1021/acs.nanolett.4c03029. IF: 9.600
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Orbital Hall effect and topology on a two-dimensional triangular lattice: From bulk to edge
Barbosa, Anderson L R; Canonico, Luis M; Garcia, Jose H; Rappoport, Tatiana G Physical Review b; 110 (8): 085412. 2024. 10.1103/PhysRevB.110.085412. IF: 3.200
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Orbital Hall responses in disordered topological materials
Canonico, Luis M; Garcia, Jose H; Roche, Stephan Physical Review b; 110 (14): L140201. 2024. 10.1103/PhysRevB.110.L140201. IF: 3.200
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Twisting Between Topological Phases in 1D Conjugated Polymers via a Multiradical Transition State
Alcon, Isaac; Canonico, Luis Manuel; Papior, Nick; Garcia, Jose-Hugo; Cummings, Aron W; Tremblay, Jean-Christophe; Pruneda, Miguel; Brandbyge, Mads; Paulus, Beate; Roche, Stephan Advanced Functional Materials; 2024. 10.1002/adfm.202409174. IF: 18.500
2022
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Electrical control of spin-polarized topological currents in monolayer WTe2
Garcia, JH; You, JX; Garcia-Mota, M; Koval, P; Ordejon, P; Cuadrado, R; Verstraete, MJ; Zanolli, Z; Roche, S Physical Review b; 106 (16) 2022. 10.1103/PhysRevB.106.L161410. IF: 3.908
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Giant valley-polarized spin splittings in magnetized Janus Pt dichalcogenides
Sattar S., Larsson J.A., Canali C.M., Roche S., Garcia J.H. Physical Review B; 105 (4, A100) 2022. 10.1103/PhysRevB.105.L041402. IF: 4.036
We reveal giant proximity-induced magnetism and valley-polarization effects in Janus Pt dichalcogenides (such as SPtSe), when bound to the europium oxide (EuO) substrate. Using first-principles simulations, it is surprisingly found that the charge redistribution, resulting from proximity with EuO, leads to the formation of two K and K′ valleys in the conduction bands. Each of these valleys displays its own spin polarization and a specific spin texture dictated by broken inversion and time-reversal symmetries, and valley-exchange and Rashba splittings as large as hundreds of meV. This provides a platform for exploring spin-valley physics in low-dimensional semiconductors, with potential spin transport mechanisms such as spin-orbit torques much more resilient to disorder and temperature effects. © 2022 American Physical Society.
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Have mysterious topological valley currents been observed in graphene superlattices?
Roche S., Power S.R., Nikolić B.K., García J.H., Jauho A.-P. JPhys Materials; 5 (2, 021001) 2022. 10.1088/2515-7639/ac452a. IF: 0.000
We provide a critical discussion concerning the claim of topological valley currents, driven by a global Berry curvature and valley Hall effect proposed in recent literature. After pointing out a major inconsistency of the theoretical scenario proposed to interpret giant nonlocal resistance, we discuss various possible alternative explanations and open directions of research to solve the mystery of nonlocal transport in graphene superlattices. © 2022 The Author(s).
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Magnetism, symmetry and spin transport in van der Waals layered systems
Kurebayashi H., Garcia J.H., Khan S., Sinova J., Roche S. Nature Reviews Physics; 4 (3): 150 - 166. 2022. 10.1038/s42254-021-00403-5. IF: 31.068
The discovery of an ever-increasing family of atomic layered magnetic materials, together with the already established vast catalogue of strong spin–orbit coupling and topological systems, calls for some guiding principles to tailor and optimize novel spin transport and optical properties at their interfaces. Here, we focus on the latest developments in both fields that have brought them closer together and make them ripe for future fruitful synergy. After outlining fundamentals on van der Waals magnetism and spin–orbit coupling effects, we discuss how their coexistence, manipulation and competition could ultimately establish new ways to engineer robust spin textures and drive the generation and dynamics of spin current and magnetization switching in 2D-materials-based van der Waals heterostructures. Grounding our analysis on existing experimental results and theoretical considerations, we draw a prospective analysis about how intertwined magnetism and spin–orbit torque phenomena combine at interfaces with well-defined symmetries and how this dictates the nature and figures of merit of spin–orbit torque and angular momentum transfer. This will serve as a guiding role in designing future non-volatile memory devices that utilize the unique properties of 2D materials with the spin degree of freedom. © 2022, Springer Nature Limited.
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Manipulation of spin transport in graphene/transition metal dichalcogenide heterobilayers upon twisting
Pezo A., Zanolli Z., Wittemeier N., Ordejón P., Fazzio A., Roche S., Garcia J.H. 2D Materials; 9 (1, 015008) 2022. 10.1088/2053-1583/ac3378. IF: 7.103
Proximity effects between layered materials trigger a plethora of novel and exotic quantum transport phenomena. Besides, the capability to modulate the nature and strength of proximity effects by changing crystalline and interfacial symmetries offers a vast playground to optimize physical properties of relevance for innovative applications. In this work, we use large-scale first principles calculations to demonstrate that strain and twist-angle strongly vary the spin–orbit coupling (SOC) in graphene/transition metal dichalcogenide heterobilayers. Such a change results in a modulation of the spin relaxation times by up to two orders of magnitude. Additionally, the relative strengths of valley-Zeeman and Rashba SOC can be tailored upon twisting, which can turn the system into an ideal Dirac–Rashba regime or generate transitions between topological states of matter. These results shed new light on the debated variability of SOC and clarify how lattice deformations can be used as a knob to control spin transport. Our outcomes also suggest complex spin transport in polycrystalline materials, due to the random variation of grain orientation, which could reflect in large spatial fluctuations of SOC fields. © 2021 IOP Publishing Ltd
2021
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Control of spin-charge conversion in van der Waals heterostructures
Galceran R., Tian B., Li J., Bonell F., Jamet M., Vergnaud C., Marty A., García J.H., Sierra J.F., Costache M.V., Roche S., Valenzuela S.O., Manchon A., Zhang X., Schwingenschlögl U. APL Materials; 9 (10, 100901) 2021. 10.1063/5.0054865. IF: 5.096
The interconversion between spin and charge degrees of freedom offers incredible potential for spintronic devices, opening routes for spin injection, detection, and manipulation alternative to the use of ferromagnets. The understanding and control of such interconversion mechanisms, which rely on spin-orbit coupling, is therefore an exciting prospect. The emergence of van der Waals materials possessing large spin-orbit coupling (such as transition metal dichalcogenides or topological insulators) and/or recently discovered van der Waals layered ferromagnets further extends the possibility of spin-to-charge interconversion to ultrathin spintronic devices. Additionally, they offer abundant room for progress in discovering and analyzing novel spin-charge interconversion phenomena. Modifying the properties of van der Waals materials through proximity effects is an added degree of tunability also under exploration. This Perspective discusses the recent advances toward spin-to-charge interconversion in van der Waals materials. It highlights scientific developments which include techniques for large-scale growth, device physics, and theoretical aspects. © 2021 Author(s).
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Exploring billion-atom-scale quantum materials using linear scaling quantum transport
Garcia J.H. Nature Reviews Physics; 3 (6): 388. 2021. 10.1038/s42254-021-00318-1. IF: 31.068
[No abstract available]
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Janus monolayers of magnetic transition metal dichalcogenides as an all-in-one platform for spin-orbit torque
Smaili I., Laref S., Garcia J.H., Schwingenschlögl U., Roche S., Manchon A. Physical Review B; 104 (10, 104415) 2021. 10.1103/PhysRevB.104.104415. IF: 4.036
We theoretically predict that vanadium-based Janus dichalcogenide monolayers constitute an ideal platform for spin-orbit torque memories. Using first-principles calculations, we demonstrate that magnetic exchange and magnetic anisotropy energies are higher for heavier chalcogen atoms, while the broken inversion symmetry in the Janus form leads to the emergence of Rashba-like spin-orbit coupling. The spin-orbit torque efficiency is evaluated using optimized quantum transport methodology and found to be comparable to heavy nonmagnetic metals. The coexistence of magnetism and spin-orbit coupling in such materials with tunable Fermi-level opens new possibilities for monitoring magnetization dynamics in the perspective of nonvolatile magnetic random access memories. ©2021 American Physical Society.
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Linear scaling quantum transport methodologies
Fan Z., Garcia J.H., Cummings A.W., Barrios-Vargas J.E., Panhans M., Harju A., Ortmann F., Roche S. Physics Reports; 903: 1 - 69. 2021. 10.1016/j.physrep.2020.12.001. IF: 25.600
In recent years, predictive computational modeling has become a cornerstone for the study of fundamental electronic, optical, and thermal properties in complex forms of condensed matter, including Dirac and topological materials. The simulation of quantum transport in realistic models calls for the development of linear scaling, or order-N, numerical methods, which then become enabling tools for guiding experimental research and for supporting the interpretation of measurements. In this review, we describe and compare different order-N computational methods that have been developed during the past twenty years, and which have been used extensively to explore quantum transport phenomena in disordered media. We place particular focus on the zero-frequency electrical conductivities derived within the Kubo–Greenwood and Kubo–Streda formalisms, and illustrate the capabilities of these methods to tackle the quasi-ballistic, diffusive, and localization regimes of quantum transport in the noninteracting limit. The fundamental issue of computational cost versus accuracy of various proposed numerical schemes is addressed in depth. We then illustrate the usefulness of these methods with various examples of transport in disordered materials, such as polycrystalline and defected graphene models, 3D metals and Dirac semimetals, carbon nanotubes, and organic semiconductors. Finally, we extend the review to the study of spin dynamics and topological transport, for which efficient approaches for calculating charge, spin, and valley Hall conductivities are described. © 2020 The Author(s)
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Low-symmetry topological materials for large charge-to-spin interconversion: The case of transition metal dichalcogenide monolayers
Vila M., Hsu C.-H., Garcia J.H., Benítez L.A., Waintal X., Valenzuela S.O., Pereira V.M., Roche S. Physical Review Research; 3 (4, 043230) 2021. 10.1103/PhysRevResearch.3.043230. IF: 0.000
The spin polarization induced by the spin Hall effect (SHE) in thin films typically points out of the plane. This is rooted on the specific symmetries of traditionally studied systems, not in a fundamental constraint. Recently, experiments on few-layer MoTe2 and WTe2 showed that the reduced symmetry of these strong spin-orbit coupling materials enables a new form of canted spin Hall effect, characterized by concurrent in-plane and out-of-plane spin polarizations. Here, through quantum transport calculations on realistic device geometries, including disorder, we predict a very large gate-tunable SHE figure of merit λsθxy≈1-50 nm in MoTe2 and WTe2 monolayers that significantly exceeds values of conventional SHE materials. This stems from a concurrent long spin diffusion length (λs) and charge-to-spin interconversion efficiency as large as θxy≈80%, originating from momentum-invariant (persistent) spin textures together with large spin Berry curvature along the Fermi contour, respectively. Generalization to other materials and specific guidelines for unambiguous experimental confirmation are proposed, paving the way toward exploiting such phenomena in spintronic devices. These findings vividly emphasize how crystal symmetry and electronic topology can govern the intrinsic SHE and spin relaxation, and how they may be exploited to broaden the range and efficiency of spintronic materials and functionalities. © 2021 authors. Published by the American Physical Society.
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Valley Hall effect and nonlocal resistance in locally gapped graphene
Aktor T., Garcia J.H., Roche S., Jauho A.-P., Power S.R. Physical Review B; 103 (11, 115406) 2021. 10.1103/PhysRevB.103.115406. IF: 4.036
We report on the emergence of bulk, valley-polarized currents in graphene-based devices, driven by spatially varying regions of broken sublattice symmetry, and revealed by nonlocal resistance (RNL) fingerprints. By using a combination of quantum transport formalisms, giving access to bulk properties as well as multiterminal device responses, the presence of a nonuniform local band gap is shown to give rise to valley-dependent scattering and a finite Fermi-surface contribution to the valley Hall conductivity, related to characteristics of RNL. These features are robust against disorder and provide a plausible interpretation of controversial experiments in graphene/hexagonal boron nitride superlattices. Our findings suggest both an alternative mechanism for the generation of valley Hall effect in graphene and a route towards valley-dependent electron optics, by materials and device engineering. © 2021 American Physical Society.
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Valley-polarized quantum anomalous Hall phase in bilayer graphene with layer-dependent proximity effects
Vila M., Garcia J.H., Roche S. Physical Review B; 104 (16, A84) 2021. 10.1103/PhysRevB.104.L161113. IF: 4.036
Realizations of some topological phases in two-dimensional systems rely on the challenge of jointly incorporating spin-orbit and magnetic exchange interactions. Here, we predict the formation and control of a fully valley-polarized quantum anomalous Hall effect in bilayer graphene, by separately imprinting spin-orbit and magnetic proximity effects in different layers. This results in varying spin splittings for the conduction and valence bands, which gives rise to a topological gap at a single Dirac cone. The topological phase can be controlled by a gate voltage and switched between valleys by reversing the sign of the exchange interaction. By performing quantum transport calculations in disordered systems, the chirality and resilience of the valley-polarized edge state are demonstrated. Our findings provide a promising route to engineer a topological phase that could enable low-power electronic devices and valleytronic applications as well as putting forward layer-dependent proximity effects in bilayer graphene as a way to create versatile topological states of matter. © 2021 American Physical Society.
2020
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Canted Persistent Spin Texture and Quantum Spin Hall Effect in WTe2
Garcia J.H., Vila M., Hsu C.-H., Waintal X., Pereira V.M., Roche S. Physical Review Letters; 125 (25, 256603) 2020. 10.1103/PhysRevLett.125.256603. IF: 8.385
We report an unconventional quantum spin Hall phase in the monolayer WTe2, which exhibits hitherto unknown features in other topological materials. The low symmetry of the structure induces a canted spin texture in the yz plane, which dictates 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. These findings are based on large-scale quantum simulations of the spin Hall conductivity tensor and nonlocal resistances in multiprobe geometries using a realistic tight-binding model elaborated from first-principle methods. The observation of this canted quantum spin Hall effect, related to the formation of topological edge states with nontrivial spin polarization, demands for specific experimental design and suggests interesting alternatives for manipulating spin information in topological materials. © 2020 American Physical Society.
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Magnetism, spin dynamics, and quantum transport in two-dimensional systems
Savero Torres W., Sierra J.F., Benítez L.A., Bonell F., García J.H., Roche S., Valenzuela S.O. MRS Bulletin; 45 (5): 357 - 365. 2020. 10.1557/mrs.2020.121. IF: 5.061
Two-dimensional (2D) quantum materials offer a unique platform to explore mesoscopic phenomena driven by interfacial and topological effects. Their tunable electric properties and bidimensional nature enable their integration into sophisticated heterostructures with engineered properties, resulting in the emergence of new exotic phenomena not accessible in other platforms. This has fostered many studies on 2D ferromagnetism, proximity-induced effects, and quantum transport, demonstrating their relevance for fundamental research and future device applications. Here, we review ongoing progress in this lively research field with special emphasis on spin-related phenomena. © Materials Research Society 2020.
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Nonlocal Spin Dynamics in the Crossover from Diffusive to Ballistic Transport
Vila M., Garcia J.H., Cummings A.W., Power S.R., Groth C.W., Waintal X., Roche S. Physical Review Letters; 124 (19, 196602) 2020. 10.1103/PhysRevLett.124.196602. IF: 8.385
Improved fabrication techniques have enabled the possibility of ballistic transport and unprecedented spin manipulation in ultraclean graphene devices. Spin transport in graphene is typically probed in a nonlocal spin valve and is analyzed using spin diffusion theory, but this theory is not necessarily applicable when charge transport becomes ballistic or when the spin diffusion length is exceptionally long. Here, we study these regimes by performing quantum simulations of graphene nonlocal spin valves. We find that conventional spin diffusion theory fails to capture the crossover to the ballistic regime as well as the limit of long spin diffusion length. We show that the latter can be described by an extension of the current theoretical framework. Finally, by covering the whole range of spin dynamics, our study opens a new perspective to predict and scrutinize spin transport in graphene and other two-dimensional material-based ultraclean devices. © 2020 American Physical Society.
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Tunable room-temperature spin galvanic and spin Hall effects in van der Waals heterostructures
Benítez L.A., Savero Torres W., Sierra J.F., Timmermans M., Garcia J.H., Roche S., Costache M.V., Valenzuela S.O. Nature Materials; 19 (2): 170 - 175. 2020. 10.1038/s41563-019-0575-1. IF: 38.663
Spin–orbit coupling stands as a powerful tool to interconvert charge and spin currents and to manipulate the magnetization of magnetic materials through spin-torque phenomena. However, despite the diversity of existing bulk materials and the recent advent of interfacial and low-dimensional effects, control of this interconversion at room temperature remains elusive. Here, we demonstrate strongly enhanced room-temperature spin-to-charge interconversion in graphene driven by the proximity of WS2. By performing spin precession experiments in appropriately designed Hall bars, we separate the contributions of the spin Hall and the spin galvanic effects. Remarkably, their corresponding conversion efficiencies can be tailored by electrostatic gating in magnitude and sign, peaking near the charge neutrality point with an equivalent magnitude that is comparable to the largest efficiencies reported to date. Such electric-field tunability provides a building block for spin generation free from magnetic materials and for ultra-compact magnetic memory technologies. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.
2019
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Room-Temperature Spin Hall Effect in Graphene/MoS 2 van der Waals Heterostructures
Safeer C.K., Ingla-Aynés J., Herling F., Garcia J.H., Vila M., Ontoso N., Calvo M.R., Roche S., Hueso L.E., Casanova F. Nano Letters; 2019. 10.1021/acs.nanolett.8b04368. IF: 12.279
Graphene is an excellent material for long-distance spin transport but allows little spin manipulation. Transition-metal dichalcogenides imprint their strong spin-orbit coupling into graphene via the proximity effect, and it has been predicted that efficient spin-to-charge conversion due to spin Hall and Rashba-Edelstein effects could be achieved. Here, by combining Hall probes with ferromagnetic electrodes, we unambiguously demonstrate experimentally the spin Hall effect in graphene induced by MoS 2 proximity and for varying temperatures up to room temperature. The fact that spin transport and the spin Hall effect occur in different parts of the same material gives rise to a hitherto unreported efficiency for the spin-to-charge voltage output. Additionally, for a single graphene/MoS 2 heterostructure-based device, we evidence a superimposed spin-to-charge current conversion that can be indistinguishably associated with either the proximity-induced Rashba-Edelstein effect in graphene or the spin Hall effect in MoS 2 . By a comparison of our results to theoretical calculations, the latter scenario is found to be the most plausible one. Our findings pave the way toward the combination of spin information transport and spin-to-charge conversion in two-dimensional materials, opening exciting opportunities in a variety of future spintronic applications. © 2019 American Chemical Society.
2018
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Charge and spin transport anisotropy in nanopatterned graphene
Gregersen, Soren Schou; Garcia, Jose H.; Jauho, Antti-Pekka; Roche, Stephan; Power, Stephen R.; Journal Of Physics-Materials; 1 (1) 2018. 10.1088/2515-7639/aadca3.
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Deciphering the origin of nonlocal resistance in multiterminalgraphene on hexagonal-boron-nitride withab initioquantumtransport: Fermi surface edge currents rather than Fermi seatopological valley currents
J M Marmolejo-Tejada, J H García, M D Petrovic, P-H Chang, X-L Sheng, A Cresti, P Plechác, S Roche and B K Nikolic Journal of Physics: Materials; 1 (1) 2018. 10.1088/2515-7639/aad585.
The recent observation (Gorbachev et al 2014 Science 346 448) of nonlocal resistance R NL near the Dirac point (DP) of multiterminal graphene on aligned hexagonal-boron nitride (G/hBN) has been interpreted as the consequence of topological valley Hall currents carried by the Fermi sea states just beneath the bulk gap E g induced by inversion symmetry breaking. However, the corresponding valley Hall conductivity ${\sigma }_{{xy}}^{v}$, quantized inside E g , is not directly measurable. Conversely, the Landauer–Büttiker formula, as a numerically exact approach to observable nonlocal transport quantities, yields R NL ≡ 0 for the same simplistic Hamiltonian of gapped graphene that generates ${\sigma }_{{xy}}^{v}\ne 0$ via the Kubo formula. We combine ab initio with quantum transport calculations to demonstrate that G/hBN wires with zigzag edges host dispersive edge states near the DP that are absent in theories based on the simplistic Hamiltonian. Although such edge states exist also in isolated zigzag graphene wires, aligned hBN is required to modify their energy–momentum dispersion and generate ${R}_{\mathrm{NL}}\ne 0$ near the DP. The Fermi surface-determined edge currents carrying the nonlocal signal persist also in the presence of edge disorder and over long distances. Concurrently, they resolve the long-standing puzzle of why the highly insulating state of G/hBN is rarely observed. Thus, we conclude that the observed R NL is unrelated to Fermi sea topological valley currents conjectured for gapped Dirac spectra.
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Finite-size correction scheme for supercell calculations in Dirac-point two-dimensional materials
Rocha C.G., Rocha A.R., Venezuela P., Garcia J.H., Ferreira M.S. Scientific Reports; 8 (1, 9348) 2018. 10.1038/s41598-018-27632-6. IF: 4.122
Modern electronic structure calculations are predominantly implemented within the super cell representation in which unit cells are periodically arranged in space. Even in the case of non-crystalline materials, defect-embedded unit cells are commonly used to describe doped structures. However, this type of computation becomes prohibitively demanding when convergence rates are sufficiently slow and may require calculations with very large unit cells. Here we show that a hitherto unexplored feature displayed by several 2D materials may be used to achieve convergence in formation- A nd adsorption-energy calculations with relatively small unit-cell sizes. The generality of our method is illustrated with Density Functional Theory calculations for different 2D hosts doped with different impurities, all of which providing accuracy levels that would otherwise require enormously large unit cells. This approach provides an efficient route to calculating the physical properties of 2D systems in general but is particularly suitable for Dirac-point materials doped with impurities that break their sublattice symmetry. © 2018 The Author(s).
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Large spin relaxation anisotropy and valley-Zeeman spin-orbit coupling in WSe2 /graphene/ h -BN heterostructures
Zihlmann S., Cummings A.W., Garcia J.H., Kedves M., Watanabe K., Taniguchi T., Schönenberger C., Makk P. Physical Review B; 97 (7, 075434) 2018. 10.1103/PhysRevB.97.075434. IF: 3.813
Large spin-orbital proximity effects have been predicted in graphene interfaced with a transition-metal dichalcogenide layer. Whereas clear evidence for an enhanced spin-orbit coupling has been found at large carrier densities, the type of spin-orbit coupling and its relaxation mechanism remained unknown. We show an increased spin-orbit coupling close to the charge neutrality point in graphene, where topological states are expected to appear. Single-layer graphene encapsulated between the transition-metal dichalcogenide WSe2 and h-BN is found to exhibit exceptional quality with mobilities as high as 1×105 cm2 V-1 s-1. At the same time clear weak antilocalization indicates strong spin-orbit coupling, and a large spin relaxation anisotropy due to the presence of a dominating symmetric spin-orbit coupling is found. Doping-dependent measurements show that the spin relaxation of the in-plane spins is largely dominated by a valley-Zeeman spin-orbit coupling and that the intrinsic spin-orbit coupling plays a minor role in spin relaxation. The strong spin-valley coupling opens new possibilities in exploring spin and valley degree of freedom in graphene with the realization of new concepts in spin manipulation. © 2018 American Physical Society.
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Quantum Hall effect in graphene with interface-induced spin-orbit coupling
Cysne T.P., Garcia J.H., Rocha A.R., Rappoport T.G. Physical Review B; 97 (8, 085413) 2018. 10.1103/PhysRevB.97.085413. IF: 3.813
We consider an effective model for graphene with interface-induced spin-orbit coupling and calculate the quantum Hall effect in the low-energy limit. We perform a systematic analysis of the contribution of the different terms of the effective Hamiltonian to the quantum Hall effect (QHE). By analyzing the spin splitting of the quantum Hall states as a function of magnetic field and gate voltage, we obtain different scaling laws that can be used to characterize the spin-orbit coupling in experiments. Furthermore, we employ a real-space quantum transport approach to calculate the quantum Hall conductivity and investigate the robustness of the QHE to disorder introduced by hydrogen impurities. For that purpose, we combine first-principles calculations and a genetic algorithm strategy to obtain a graphene-only Hamiltonian that models the impurity. © 2018 American Physical Society.
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Shubnikov-de Haas oscillations in the anomalous Hall conductivity of Chern insulators
Canonico L.M., García J.H., Rappoport T.G., Ferreira A., Muniz R.B. Physical Review B; 98 (8, 085409) 2018. 10.1103/PhysRevB.98.085409. IF: 3.813
The Haldane model on a honeycomb lattice is a paradigmatic example of a system featuring quantized Hall conductivity in the absence of an external magnetic field, that is, a quantum anomalous Hall effect. Recent theoretical work predicted that the anomalous Hall conductivity of massive Dirac fermions can display Shubnikov-de Haas (SdH) oscillations, which could be observed in topological insulators and honeycomb layers with strong spin-orbit coupling. Here, we investigate the electronic transport properties of Chern insulators subject to high magnetic fields by means of accurate spectral expansions of lattice Green's functions. We find that the anomalous component of the Hall conductivity displays visible SdH oscillations at low temperature. The effect is shown to result from the modulation of the next-nearest-neighbor flux accumulation due to the Haldane term, which removes the electron-hole symmetry from the Landau spectrum. To support our numerical findings, we derive a long-wavelength description beyond the linear ("Dirac cone") approximation. Finally, we discuss the dependence of the energy spectra shift for reversed magnetic fields with the topological gap and the lattice bandwidth. © 2018 American Physical Society.
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Spin transport in graphene/transition metal dichalcogenide heterostructures
Garcia J.H., Vila M., Cummings A.W., Roche S. Chemical Society Reviews; 47 (9): 3359 - 3379. 2018. 10.1039/c7cs00864c. IF: 40.182
Since its discovery, graphene has been a promising material for spintronics: its low spin-orbit coupling, negligible hyperfine interaction, and high electron mobility are obvious advantages for transporting spin information over long distances. However, such outstanding transport properties also limit the capability to engineer active spintronics, where strong spin-orbit coupling is crucial for creating and manipulating spin currents. To this end, transition metal dichalcogenides, which have larger spin-orbit coupling and good interface matching, appear to be highly complementary materials for enhancing the spin-dependent features of graphene while maintaining its superior charge transport properties. In this review, we present the theoretical framework and the experiments performed to detect and characterize the spin-orbit coupling and spin currents in graphene/transition metal dichalcogenide heterostructures. Specifically, we will concentrate on recent measurements of Hanle precession, weak antilocalization and the spin Hall effect, and provide a comprehensive theoretical description of the interconnection between these phenomena. © 2018 The Royal Society of Chemistry.
2017
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A DETERMINISTIC APPROACH TO THE SYNCHRONIZATION OF NONLINEAR CELLULAR AUTOMATA
De Abreu J., García P., García J. Advances in Complex Systems; 20 (4-5, 1750006) 2017. 10.1142/S0219525917500060.
In this work, we introduce a deterministic scheme of synchronization of nonlinear cellular automata with chaotic behavior, connected through a master-slave coupling. By using a definition of Boolean derivative, we utilize the linear approximation of the cellular automata rules to design a deterministic and simple coupling function that ensures synchronization. Our results show that it is possible to synchronize nonlinear chaotic cellular automata using a deterministic coupling function that does not introduce into the slave all the information about the state of the master. © 2017 World Scientific Publishing Company.