In the chapter 3, we study ferromagnetic fluctuations on two types of bilayer triangular lattices by the single-band Hubbard model. We start from the tight-binding model to obtain energy spectrum, the density of sates, and the spin susceptibility. With finite Coulomb interaction turned on, we apply the random phase approximation and use the determinant quantum Monte Carlo method to study spin susceptibility for the two bilayer triangular lattices and make comparisons of their magnetic properties. The effects of the interlayer coupling is also examined in detail. / In the chapter 4, we addresses the issue of the ferromagnetism in graphene-based samples. To study magnetic correlations in graphene, we systematically carry out quantum Monte Carlo simulations of the Hubbard model on a honeycomb lattice. In the filling region below the Van Hove singularity, the system shows a short-range ferromagnetic correlation, which is slightly strengthened by the on-site Coulomb interaction and markedly by the next-nearest-neighbor hopping integral. The ferromagnetic properties depend on the electron filling strongly, which may be manipulated by the electric gate. Due to its resultant high controllability of ferromagnetism, graphene-based samples may facilitate the new development of many applications. / In the chapter 5, we examined theoretically the magnetism of impurity adatoms in graphene by quantum Monte Carlo simulation technique based on Hirsch-Fye algorithm. When tuning the Fermi energy of graphene by gate voltage with available experiments, the values of occupancy and local moment for impurity can be changed. Furthermore, with medium and large hybridizations between impurity and graphene atoms, the local moment can be switched on and off by Kondo effects. We also use maximum entropy method to study the spectral density from Green's function for impurity, and we find very unconventional behaviors which are absolutely different from the cases in the normal metal. These signatures of spectral density enlarge the possibility for controlling the impurity magnetism by gate voltage. / In this research thesis, we mainly study three strongly correlated systems: Hubbard model in bilayer triangular lattice which corresponds to the real material of NaxCoO2 · yH 2O, strong-interaction electrons in graphene system and Anderson impurity in graphene. Our numerical method is determinant quantum Monte Carlo method which will be introduced in the chapter 2. / Hu, Feiming = 阻錯系統的量子門特卡洛研究 / 胡飛鳴. / Adviser: Lin Hai-Qing. / Source: Dissertation Abstracts International, Volume: 73-01, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 107-126). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Hu, Feiming = Zu cuo xi tong de liang zi Mente Kaluo yan jiu / Hu Feiming.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_344628 |
| Date | January 2010 |
| Contributors | Hu, Feiming., Chinese University of Hong Kong Graduate School. Division of Physics. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, theses |
| Format | electronic resource, microform, microfiche, 1 online resource (xix, 126 leaves : ill.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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