Spin-Hall effect in topological materials: evaluating the proper spin current in systems with arbitrary degeneracies
Abstract The spin-Hall effect underpins some of the most active topics in modern physics, including spin torques and the inverse spin-Hall effect, yet it lacks a proper theoretical description. This makes it difficult to differentiate the SHE from other mechanisms, as well as differentiate band stru...
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| Format: | Article |
| Language: | English |
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Nature Portfolio
2024-11-01
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| Series: | npj Spintronics |
| Online Access: | https://doi.org/10.1038/s44306-024-00057-w |
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| author | Hongyang Ma James H. Cullen Serajum Monir Rajib Rahman Dimitrie Culcer |
| author_facet | Hongyang Ma James H. Cullen Serajum Monir Rajib Rahman Dimitrie Culcer |
| author_sort | Hongyang Ma |
| collection | DOAJ |
| description | Abstract The spin-Hall effect underpins some of the most active topics in modern physics, including spin torques and the inverse spin-Hall effect, yet it lacks a proper theoretical description. This makes it difficult to differentiate the SHE from other mechanisms, as well as differentiate band structure and disorder contributions. Here, by exploiting recent analytical breakthroughs in the understanding of the intrinsic spin-Hall effect, we devise a density functional theory method for evaluating the conserved (proper) spin current in a generic system. Spin non-conservation makes the conventional spin current physically meaningless, while the conserved spin current has been challenging to evaluate since it involves the position operator between Bloch bands. The novel method we introduce here can handle band structures with arbitrary degeneracies and incorporates all matrix elements of the position operator, including the notoriously challenging diagonal elements, which are associated with Fermi surface, group velocity, and dipolar effects but often diverge if not treated correctly. We apply this method to the most important classes of spin-Hall materials: topological insulators, 2D quantum spin-Hall insulators, non-collinear antiferromagnets, and strongly spin-orbit coupled metals. We demonstrate that the torque dipole systematically suppresses contributions to the conventional spin current such that, the proper spin current is generally smaller in magnitude and often has a different sign. Remarkably, its energy-dependence is relatively flat and featureless, and its magnitude is comparable in all classes of materials studied. These findings will guide the experiment in characterizing charge-to-spin interconversion in spintronic and orbitronic devices. We also discuss briefly a potential generalization of the method to calculate extrinsic spin currents generated by disorder scattering. |
| format | Article |
| id | doaj-art-c0b52c49c7134e74bf8b12a95fc9d557 |
| institution | Kabale University |
| issn | 2948-2119 |
| language | English |
| publishDate | 2024-11-01 |
| publisher | Nature Portfolio |
| record_format | Article |
| series | npj Spintronics |
| spelling | doaj-art-c0b52c49c7134e74bf8b12a95fc9d5572024-11-24T12:08:54ZengNature Portfolionpj Spintronics2948-21192024-11-012111010.1038/s44306-024-00057-wSpin-Hall effect in topological materials: evaluating the proper spin current in systems with arbitrary degeneraciesHongyang Ma0James H. Cullen1Serajum Monir2Rajib Rahman3Dimitrie Culcer4School of Physics, The University of New South WalesSchool of Physics, The University of New South WalesSchool of Physics, The University of New South WalesSchool of Physics, The University of New South WalesSchool of Physics, The University of New South WalesAbstract The spin-Hall effect underpins some of the most active topics in modern physics, including spin torques and the inverse spin-Hall effect, yet it lacks a proper theoretical description. This makes it difficult to differentiate the SHE from other mechanisms, as well as differentiate band structure and disorder contributions. Here, by exploiting recent analytical breakthroughs in the understanding of the intrinsic spin-Hall effect, we devise a density functional theory method for evaluating the conserved (proper) spin current in a generic system. Spin non-conservation makes the conventional spin current physically meaningless, while the conserved spin current has been challenging to evaluate since it involves the position operator between Bloch bands. The novel method we introduce here can handle band structures with arbitrary degeneracies and incorporates all matrix elements of the position operator, including the notoriously challenging diagonal elements, which are associated with Fermi surface, group velocity, and dipolar effects but often diverge if not treated correctly. We apply this method to the most important classes of spin-Hall materials: topological insulators, 2D quantum spin-Hall insulators, non-collinear antiferromagnets, and strongly spin-orbit coupled metals. We demonstrate that the torque dipole systematically suppresses contributions to the conventional spin current such that, the proper spin current is generally smaller in magnitude and often has a different sign. Remarkably, its energy-dependence is relatively flat and featureless, and its magnitude is comparable in all classes of materials studied. These findings will guide the experiment in characterizing charge-to-spin interconversion in spintronic and orbitronic devices. We also discuss briefly a potential generalization of the method to calculate extrinsic spin currents generated by disorder scattering.https://doi.org/10.1038/s44306-024-00057-w |
| spellingShingle | Hongyang Ma James H. Cullen Serajum Monir Rajib Rahman Dimitrie Culcer Spin-Hall effect in topological materials: evaluating the proper spin current in systems with arbitrary degeneracies npj Spintronics |
| title | Spin-Hall effect in topological materials: evaluating the proper spin current in systems with arbitrary degeneracies |
| title_full | Spin-Hall effect in topological materials: evaluating the proper spin current in systems with arbitrary degeneracies |
| title_fullStr | Spin-Hall effect in topological materials: evaluating the proper spin current in systems with arbitrary degeneracies |
| title_full_unstemmed | Spin-Hall effect in topological materials: evaluating the proper spin current in systems with arbitrary degeneracies |
| title_short | Spin-Hall effect in topological materials: evaluating the proper spin current in systems with arbitrary degeneracies |
| title_sort | spin hall effect in topological materials evaluating the proper spin current in systems with arbitrary degeneracies |
| url | https://doi.org/10.1038/s44306-024-00057-w |
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