Ferromagnetic Instability in an Almost Hall-filled s-band

• Main Authors: Liang-Chi Kuo, 郭良吉
• Other Authors: Wei-Neng Huang
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/92777027969512416924

碩士 === 中原大學 === 應用物理研究所 === 90 === Abstract After the fact that the ferromagnetic state with one hole in a narrow band is ground state has been verified, next comes the question whether the ferromagnetic state with two holes is still the ground state. Researchers have presented diverse ways of taking approximations and doing calculation, but there is no rigorous proof for two holes, and the stability of the ferromagnetic state is still an unsolved problem. In this thesis, we use Hubbard model, which is presented in 1963 and tight binding method for energy bands to study the problem. The model is determined by a nearest-neighbor transfer matrix t and on-site repulsion U. We take further limit U= to simplify the consideration. In conclusion, for two holes, we are able to obtain a singlet state with lower energy than that of ferromagnetic state. The ferromagnetic state is no longer the ground state as soon as two holes are present.