Spin Gap of Two-Dimensional Antiferromagnet Representing CaV${}_4$O${}_9$

Kazuhiro Sano, Ken'ichi Takano

We examined a two-dimensional Heisenberg model with two kinds of exchange energies, $J_e$ and $J_c$. This model describes localized spins at vanadium ions in a layer of CaV${}_4$O$_9…