A phase transition in a solid is produced by the order-disorder transition of any of the four fundamental degrees of freedom (orbital, spin, lattice and charge). Recently, there has been increasing interest in systems where more than two degrees of freedom are coupled. Tl2Ru2O7 shows clear anomalies around 125K in its bulk properties, and we have undertaken both elastic and inelastic neutron scattering studies to help understand this behaviour. According to our neutron diffraction experiments, Tl2Ru2O7 undergoes a cubic-orthorhombic structural transition with three different types of Ru-Ru bond distances and the shortest zig-zag bond running along the b-axis. Our inelastic neutron experiments also revealed that there is evidence of a spin gap with a gap energy of 11meV. With insights produced from band calculations, we discovered that all these observations can be understood in terms of one dimensional Ru 4d orbital ordering below 125K. The coupling to its spin and lattice degrees of freedom then leads to the spin gap and structural distortion.
S Lee, J-G Park (Sungkyunkwan University, South Korea), DT Adroja (ISIS), D Khomskii (University of Koln, Germany) , KA McEwen (University College London), S Streltsov, VI Anisimov (Institute of Metal Physics), R Ibberson (ISIS), K Yoshimura (Kyoto University, Japan)
Research date: December 2006
Prof J-G Park, [firstname.lastname@example.org] Seongsu Lee et al., Nature Materials 5 (2006) 471