| 研究領域 | J-Physics：多極子伝導系の物理 |
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| 研究課題/領域番号 |
18H04316
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| 研究機関 | 京都大学 |
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研究代表者 |
Peters Robert 京都大学, 理学研究科, 講師 (80734293)
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| 研究期間 (年度) |
2018-04-01 – 2020-03-31
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| キーワード | f-electron materials / spin-orbit interaction / non-centrosymmetric / Rashba interaction / Kondo effect / spintronics |
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| 研究実績の概要 |
The combination of strong spin-orbit coupling and strong correlations holds tremendous potential for interesting physical phenomena as well as applications in spintronics and quantum computation. We here are studying the interplay between the Rashba spin-orbit coupling and the Kondo screening in non-centrosymmetric f-electron materials. By using perturbation theory, we have shown that the Kondo screening in non-centrosymmetric f-electron systems becomes anisotropic, which can lead to a reduction of the Kondo temperature or even to a quantum critical point.
As commonly observed in systems with Rashba spin-orbit interaction, we observe bands with helical spin-texture; the spin is clockwise or anticlockwise locked to the momentum in the Brillouin zone. Remarkably, we have shown that the interplay between local and nonlocal c-f hybridization in non-centrosymmetric systems results in different strengths of the hybridization depending on the spin-texture of the band; while the hybridization is enhanced for one band, it is reduced in the other. This can even lead to the formation of a half-metallic helical metal, where only one of the helical bands is present at the Fermi energy. Contrary to noninteracting systems, the band structure in non-centrosymmetric f-electron systems changes with temperature. Because of the dependence of the hybridization on the helical spin direction, the Kondo effect and the resulting changes in the band structure manifest themselves differently depending on the spin-texture, which may be used in spintronic applications.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
By using perturbation theory, it became clear that certain effects of a momentum dependent hybridization are not taken correctly into account in a usual dynamical mean field calculation. Perturbation theory shows that a momentum dependent hybridization will lead in non-centrosymmetric f-electron systems to an anisotropic Kondo coupling, which can result in the reduction of the Kondo temperature or even in a quantum critical point for a single Kondo impurity.
Thus, several interesting questions arise in the context of non-centrosymmetric f-electron materials: Is the reduction of the Kondo temperature visible in f-electron materials, where every atom includes f-electrons; are there other effects due to the anisotropic Kondo coupling; can there be a quantum critical point in the f-electron material. Although these are very interesting questions, it became clear that these questions cannot be clarified using usual dynamical mean field theory.
Currently, I am working on a two-site model, which can correctly describe the anisotropic situation arising from a momentum dependent hybridization. Using this model, I think I will be able to answer the above-raised questions. First, I plan to analyze the anisotropy effects due to the momentum dependent hybridization in a two-impurity model. Such a two-impurity model is the basic ingredient for later cluster dynamical mean field calculations for non-centrosymmetric f-electron materials. The calculations for the two-impurity model are currently running.
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| 今後の研究の推進方策 |
The anisotropic Kondo coupling resulting from the momentum-dependent hybridization in non-centrosymmetric f-electron materials is an interesting effect which should be studied in more detail. As this anisotropy will affect the spin properties and can lead to quantum critical behavior, it might also be interesting in the context of spintronic applications.
I am currently analyzing the significance of a momentum dependent hybridization in a two-site impurity model. The next step is to use this model as an ingredient for cluster dynamical mean field calculations for non-centrosymmetric f-electron systems. I expect that these calculations can start very soon.
Another important topic of this project is the analysis of the interplay between the Rashba interaction and strong correlation arising at interfaces in f-electron superlattices and at open surfaces. At such an interface, the local inversion symmetry is broken, which leads to the appearance of the Rashba interaction. It has been shown in experiments for f-electron superlattices, that this Rashba interaction has interesting consequences for the superconducting and magnetic properties of the material. Currently, I am setting up a realistic model of an f-electron material at an interface, including the Rashba interaction. The model is based on first principles and thus correctly describes the situation at an interface. Using this model, I will perform real-space dynamical mean field calculation for f-electron superlattices and open surfaces and study the interplay between the Kondo effect and the Rashba interaction.
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