A Possible Phase Transition in beta-pyrochlore Compounds

Abstract

We investigate a lattice of interacting anharmonic oscillators by using a mean field theory and exact diagonalization. We construct an effective five-state hopping model with intersite repulsions as a model for beta-pyrochlore AOs_2O_6(A=K, Rb or Cs). We obtain the first order phase transition line from large to small oscillation amplitude phases as temperature decreases. We also discuss the possibility of a phase with local electric polarizations. Our theory can explain the origin of the mysterious first order transition in KOs_2O_6.

4 pages, 4 figures, submitted to J. Phys. Soc. Jpn

References in corpus (5)

• Extremely strong-coupling superconductivity and anomalous lattice properties in the beta-pyrochlore oxide KOs2O6
• NMR relaxation and resistivity from rattling phonons in pyrochlore superconductors
• Neutron Scattering Study of the Localized Mode in the beta-Pyrochlore Superconductors AOs2O6
• Superconducting Transition in the $\beta$-Pyrochlore AOs${}_2$O${}_6$ (A=Cs, Rb, K) under Pressure
• Theory of Ultrasonic Dispersion in Local Phonon Systems Coupled with Conduction Electrons