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S=1磁性体における磁気励起
https://doi.org/10.15102/1394.00002589
https://doi.org/10.15102/1394.00002589043ba748-34c3-4c5c-ba91-e1b60257df56
名前 / ファイル | ライセンス | アクション |
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Item type | 学位論文 / Thesis or Dissertation(1) | |||||||
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公開日 | 2022-12-07 | |||||||
タイトル | ||||||||
言語 | ja | |||||||
タイトル | S=1磁性体における磁気励起 | |||||||
タイトル | ||||||||
言語 | en | |||||||
タイトル | Spin–1 Magnets and Their Excitations | |||||||
言語 | ||||||||
言語 | eng | |||||||
資源タイプ | ||||||||
資源タイプ識別子 | http://purl.org/coar/resource_type/c_db06 | |||||||
資源タイプ | doctoral thesis | |||||||
ID登録 | ||||||||
ID登録 | 10.15102/1394.00002589 | |||||||
ID登録タイプ | JaLC | |||||||
アクセス権 | ||||||||
アクセス権 | open access | |||||||
アクセス権URI | http://purl.org/coar/access_right/c_abf2 | |||||||
著者 (英) |
Remund, Kimberly
× Remund, Kimberly
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抄録 | ||||||||
内容記述タイプ | Other | |||||||
内容記述 | Nature sometimes arranges itself in extremely curious ways, sowing the seed of very intriguing physics. Magnetic systems offer a rich variety of interesting features. They are traditionally studied in either their classical (S ! 1), or their extreme quantum limit (S = 12). However, magnetic degrees of freedom in spin systems span within a whole spectrum range and do not necessarily reduce to the specific case found at the extremities. Spin–1 magnets provide a good example of what happens to ground state and excitations properties for such instance. Indeed, a spin–1 is special, in the sense that, besides displaying dipolar degrees of freedom, a spin–1 can also exhibit on-site quadrupolar degrees of freedom, while retaining its quantum characteristics. Therefore, spin–1 systems are often used as examples to refer to spin-nematic order in magnetic insulators, Fe-based superconductors, or cold atoms. Unlike for spin–1 2, which in the classical limit can be represented by an O(3) vector, for spin–1, an O(3) vector does not completely describe all of what a spin–1 can do, namely intrinsically exhibiting quadrupoles. In this Thesis, I develop a united framework that enables us to treat dipolar and quadrupolar degrees of freedom of a spin–1 moment on an equal footing. My method is based on the extension of the usual su(3) algebra describing a quantum spin–1 into the u(3) algebra. Within the u(3) formalism, I derive equations of motion (EoM) for the objects living in the u(3) algebra. The u(3) approach enables the appropriate formulation for both classical and quantum derivations. Moreover, the EoM take a simple form suitable for numerical implementation. I illustrate this method by applying it to the well-known Bilinear-Biquadratic model on the triangular lattice for the ferroquadupolar state. This study is supported through classical low-temperature expansion in order to probe the thermodynamical properties, as well as quantum multi-bosons theory that allows to access dynamics. These results are validated by comparison with numerical simulations classical Monte Carlo (MC) and Molecular Dynamics (MD) respectively, both expressed in terms of u(3) objects. I show that at sufficiently low temperature numerical simulations can be corrected for the classical statistics, and the fully quantum zero-temperature analytical results are retrieved. Additionally, I confirm that our method is also applicable to anisotropic models, which is of experimental relevance. Finally, some new ideas, including the description of topological defects in spin–1 magnets and the generalization of the commonly used Self-Consistent Gaussian Approximation to the degrees of freedom of a spin–1 expressed within our u(3) framework are explored. | |||||||
口頭試問日 | ||||||||
2022-09-26 | ||||||||
学位授与年月日 | ||||||||
学位授与年月日 | 2022-11-30 | |||||||
学位名 | ||||||||
学位名 | Doctor of Philosophy | |||||||
学位授与番号 | ||||||||
学位授与番号 | 甲第112号 | |||||||
学位授与機関 | ||||||||
学位授与機関識別子Scheme | kakenhi | |||||||
学位授与機関識別子 | 38005 | |||||||
学位授与機関名 | Okinawa Institute of Science and Technology Graduate University | |||||||
著者版フラグ | ||||||||
出版タイプ | VoR | |||||||
出版タイプResource | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |||||||
権利 | ||||||||
権利情報 | © 2022 The Author |