日 時：2010年5月21日(金) 16:30-
講 師：Dr. Karlo Penc
Research Institute for Solid State Physics and Optics (Budapest, Hungary)
題 目：Symmetry breaking in the presence of Dzyaloshinskii-Moriya interactions
In the absence of the spin-orbital coupling, the configuration space of the spins is decoupled from the lattice, leading to isotropic spin models like the Heisenberg model. Phase transitions are usually related with the breaking of the continuous O(3) symmetry. However, in many materials we may not neglect the anisotropies that themselves break the O(3) symmetry of the Hamiltonian. Here we will discuss the effect of the intersite anisotropic term – the Dzyaloshinskii-Moriya interaction – in several systems: spin ladders, the orthogonal dimer model of Shastry-Sutherland, and molecular magnets. Among others, we find that in some cases the DM interaction may introduce competition that leads to the appearance of Ising phases in spin-1/2 dimer systems.
紹介教員：今田 正俊 教授、求 幸年 准教授