Spin waves and revised crystal structure of honeycomb iridate Na2IrO3
ArXiv 1202.1268 (2012)
Abstract:
We report inelastic neutron scattering measurements on Na2IrO3, a candidate for the Kitaev spin model on the honeycomb lattice. We observe spin-wave excitations below 5 meV with a dispersion that can be accounted for by including substantial further-neighbor exchanges that stabilize zig-zag magnetic order. The onset of long-range magnetic order below 15.3 K is confirmed via the observation of oscillations in zero-field muon-spin rotation experiments. Combining single-crystal diffraction and density functional calculations we propose a revised crystal structure model with significant departures from the ideal 90 deg Ir-O-Ir bonds required for dominant Kitaev exchange.Quantum criticality in an Ising chain: experimental evidence for emergent E8 symmetry
(2011)
Anomalous high-energy spin excitations in the high-Tc superconductor-parent antiferromagnet La₂CuO₄.
Phys Rev Lett 105:24 (2010) 247001
Abstract:
Inelastic neutron scattering is used to investigate the collective magnetic excitations of the high-temperature superconductor-parent antiferromagnet La2CuO4. We find that while the lower energy excitations are well described by spin-wave theory, including one- and two-magnon scattering processes, the high-energy spin waves are strongly damped near the (1/2, 0) position in reciprocal space and merge into a momentum dependent continuum. This anomalous damping indicates the decay of spin waves into other excitations, possibly unbound spinon pairs.Direct observation of charge order in triangular metallic AgNiO2 by single-crystal resonant X-ray scattering
(2010)