ORIGIN OF SPIN GAP IN CAV4O9 - EFFECTS OF FRUSTRATION AND LATTICE-DISTORTIONS

Spin gap behavior of CaV4O9 is studied by including the effects of fru strating magnetic interactions and lattice distortions. The spectrum o f triplet excitations is calculated for a Heisenberg model on the 1/5- depleted square lattice. In the spin gap phase, the location of the mi nima of the spectrum in the Brillouin zone is found to depend nontrivi ally on the exchange parameters. Experimental consequences of the temp erature-dependent lattice distortion including its effect on the unifo rm susceptibility and the spin gap are explored.