title: Disorder-Driven Spin-Orbital Liquid Behavior in the Ba3XSb2O9 Materials.
abstract: Recent experiments on the Ba(3)XSb(2)O(9) family have revealed materials that potentially realize spin- and spin-orbital liquid physics. However, the lattice structure of these materials is complicated due to the presence of charged X(2+)-Sb(5+) dumbbells, with two possible orientations. To model the lattice structure, we consider a frustrated model of charged dumbbells on the triangular lattice, with long-range Coulomb interactions. We study this model using Monte Carlo simulation, and find a freezing temperature, T(frz), at which the simulated structure factor matches well to low-temperature x-ray diffraction data for Ba(3)CuSb(2)O(9). At T=T(frz) we find a complicated "branching" structure of superexchange-linked X(2+) clusters, which form a fractal pattern with fractal dimension d(f)=1.90. We show that this gives a natural explanation for the presence of orphan spins. Finally we provide a plausible mechanism by which such dumbbell disorder can promote a spin-orbital resonant state with delocalized orphan spins.
authors.affiliation: Institut de Théorie des Phénomènes Physiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Andrew
authors.initials: A
authors.lastname: Smerald
authors.affiliation: Institut de Théorie des Phénomènes Physiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Mila