Theory of co-operative Jahn-Teller distortions in DyVO4and TbVO4(Phase transitions)

Abstract
Low temperature crystallographic phase transitions in DyVO4 and TbVO are attributed to a co-operative Jahn-Teller effect. A preliminary report of the theory is given, based on a harmonic oscillator Hamiltonian for the crystal and an electron lattice coupling which is small compared to typical phonon zero point energies. An Ising Hamiltonian is shown to describe the co-operative ordering.