The application of the mean-field theory of Schwinger bosons to the spiral spin systems

• Main Authors: Wei-Cheng Su, 蘇偉誠
• Other Authors: Chong-Der Hu
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/27139469680609213538

碩士 === 國立臺灣大學 === 物理研究所 === 100 === We have analyzed the quantum Heisenberg model on the two and three dimensional Bravais lattice in the spiral spin state using the Schwinger boson mean-field theory. By diagonalizing the system’s Hamiltonian, we obtain the general form of the mean-field free energy and the low-lying excitation dispersion relation, and then can find its magnetic order parameters. We have also found the surprising relation between the (anti)ferromagnetic order parameters and the spin quantum order by this model. It can reduce the number of variables in the calculating process. Next, we apply this model to the real systems such as RMnO3 (R denoting rare-earth ions) lattice structure to calculate the Neel temperature and other physical quantities. Below this temperature Bose-Einstein condensation of Schwinger bosons can occur. We find that it has good agreement with the experiment results.