分子フォトセミナー・物性セミナー

日時:11月4日(火)午後5時00分
場所:神戸大学 理学部Z棟103室
講師:Dr. Karlo Penc, Research Institute for Theoretical Solid State Physics and Optics, Budapest, Hungary
講演題目:Quadrupolar Phases of the S=1 Heisenberg Model on the Triangular and Square Lattice
要旨: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 zerofield the quantum fluctuations stabilize a 3-sublattice order. We also show examples of quadrupolar (nematic) ordering in classical spin system in pyrochlore lattice.