seminar given by Dr. Sungkyun Choi from Max Planck Institut für Festkörperforschung
WriterCenter for Artificial Low Dimensional Electronic Systems
RegDate2017-01-05
Hit2736
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Title: Spin dynamics and magnetic order in A2IrO3 (A=Na, Li) honeycomb iridates: implications for Kitaev physics
Abstract: We explore magnetic order and excitations in the frustrated honeycomb iridate magnets, candidates to display novel magnetic states stabilized by the strong spin-orbit coupling at the 5d Ir ions. Theory predicts composite spin-orbital Jeff=1/2 moments at the Ir ions coupled by strongly-anisotropic and bond-directional exchanges, the so-called Kitaev physics, which has in its phase diagram novel magnetically-ordered ordered phases and a quantum spin liquid with exotic excitations. To search for such physics the primary experimental technique of choice is inelastic neutron scattering to probe the spin dynamics, however this is technically very challenging due to the large absorption cross-section of neutrons by the Ir nuclei. Using an optimised setup to minimise neutron absorption, we have been successful in observing strongly dispersive spin-wave excitations of the Ir moments and results are compared with predictions for various spin Hamiltonian models including a Kitaev-Heisenberg as well as a Heisenberg model with further neighbour couplings. Moreover, we examine their crystal structures via x-ray diffraction measurements, finding various distortions away from the more idealised crystal structure which theory consider, and discuss their potential effects to the magnetism.