物理科学科セミナーご案内(2008年12月24日)
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日時 | 2008年12月24日(水)17:30〜18:30 |
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場所 | 京都産業大学理学部会議室(2号館3階) |
講演者 | Karlo Penc 氏 (京都大学基礎物理学研究所客員教授・Research Institute for Solid State Physics and Optics (RISSPO) ハンガリー) |
講演題目 | Quadrupolar Phases of the S=1 Heisenberg Model on the Triangular and Square Lattice |
講演概要
Using mean-field theory, exact diagonalizations, and SU(3) flavor theory, we have mapped out the phase diagram of the S=1 bilinear-biquadratic Heisenberg model on the triangular and square lattice in a magnetic field, with emphasis on the quadrupolar phases and their excitations. In particular, we find several plateaux phases in these models: the antiferroquadrupolar phase in the triangular lattice is characterized by a remarkable 2/3 magnetization plateau, in which one site per triangle retains quadrupolar order while the other two are polarized along the field. In the square lattice a two sublattice 1/2 plateaux develops, and at zero field the quantum fluctuations stabilize a 3-sublattice order. We also show examples of quadrupolar (nematic) ordering in classical spin system in pyrochlore lattice.