準粒子凝聚態在二維系統與自旋有序之應用

Abstract

準粒子凝聚態在凝態物理的應用廣泛，在玻色-愛因斯坦凝聚，超導體與超流體中扮演重要角色。本論文主要分為兩部分，第二至第六章討論二維半導體中激子（exciton）的凝聚態，研究顯示一種新的混合態波函數為二維半導體激子凝聚態的基態，並提供可能的實驗量測方式。 第七至第十章研究磁振子（magnon）的凝聚態，組織現有的Schwinger-boson平均場理論，應用於氧化銅材料，以及討論動量非零之玻色-愛因斯坦凝聚態之物理意義與氧化銅中commensurate-incommensurate相變生成之可能之微觀機制。

In this thesis, we study the aspects of quasiparticle condensate phenomena. The Bose-Einstein condensation of quasiparticle plays an important role in many areas such as the superconductivity, superfluidity, magnons, polaritons, and of course, one of the main topic of this thesis-exciton. The exciton condensation of two-dimensional (2D) semiconductors is reports in Ch. 2-6. We start from an effective Hamiltonian of 2D semiconductors and show an interesting mixed state of exciton condensate. The bosonization of electrons can also be a useful mathematical tool to study quantum spin systems. In Ch. 7-10, we extend the Schwinger boson mean field theory (SBMFT) method of ferromagnetic and antiferromagnetic systems. The condensation of Schwinger bosons can describe the ordering phase of spins. We study the commensurate-incommensurate phase transition of CuO as an example.