open access

https://doi.org/10.14943/doctoral.k13128

https://hdl.handle.net/2115/73151

Heisenberg 磁性体における熱励起と非弾性散乱のスピン波理論 : コンパクト化と繰り込みの新しい展開

英語

2018-03-22

Hokkaido University

50p

We propose a new scheme for modifying conventional spin waves so as to precisely describe low-dimensional Heisenberg magnets at finite temperatures. What is called the modified spin-wave theory was initiated by Takahashi, who intended to describe the low-dimensional ferromagnetic thermodynamics. There are various ways for modifying spin waves, especially, in ferrimagnets. Which magnetization should be kept zero, uniform, staggered, or both? One or more chemical potentials can be introduced so as to satisfy the relevant constraint condition either in diagonalizing the Hamiltonian or in minimizing the free energy. We can bring the thus-modified spin waves into interaction on the basis of the Hartree-Fock approximation or through the use of Wick's theorem in an attempt to refine their descriptions. Comparing various modification schemes, we eventually find an excellent bosonic language capable of describing heterogeneous quantum magnets on a variety of lattices over the whole temperature range -- Wick's-theorem-based interacting spin waves modified so as to keep every sublattice magnetization zero via the temperature-dependent Bogoliubov transformation.

2018-03-22

甲第13128号

博士(理学)

(主査) 教授 山本 昌司, 教授 根本 幸児, 講師 大原 潤, 助教 吉田 紘行

理学院（物性物理学専攻）

博士論文

Version of Record