Spontaneous formation of zigzag chains at the metal-insulator transition in the \beta-pyrochlore CsW2O6
Daigorou Hirai, Martin Bremholm, Jared M. Allred, Jason Krizan, Leslie M. Schoop, Qing Huang, Jing Tao, and R. J. Cava
Accepted
A paramagnetic metal to non-magnetic insulator transition at TMIT = 210 K is reported for the ��-pyrochlore oxide CsW2O6, accompanied by a first order structural transition that creates <110> oriented chains in the pyrochlore lattice. Comparison of CsW2O6, which has 1 electron per 2 W sites, to the fully d0 analog CsTaWO6 shows that the transitions are electronically driven. Co-refinement of high resolution synchrotron X-ray and neutron diffraction data shows that the structural distortion that creates the W chains cannot be attributed to simple charge or orbital ordering. DFT calculations suggest that the phase transition is driven by a sharply peaked electronic density of states near the Fermi energy in the cubic ��-pyrochlore phase. A further electronic instability is required to create the insulating ground state.