学术报告（7月24日）

摘要：Magnetic correlations give rise to both single electron spin-flip (magnon) and two electron spin-flip (bimagnon) excitations. In a quantum magnet bimagnon interactions are influenced both by the presence of inequivalent interactions (spatial anisotropy) and the inability to simultaneously satisfy lattice energy conditions (frustration). In recent years Resonant Inelastic X-ray Scattering (RIXS) has emerged as a powerful spectroscopic technique to study elementary excitations, including bimagnon processes, across the entire Brillouin zone in strongly correlated materials. In a typical RIXS process the energy of the incoming x-ray photon is resonantly tuned to match an element absorption edge, thus generating a large enhancement of the scattered intensity. As incident radiation loses its energy and momentum to excitations inherent to the material, direct information on the dispersions of spin, orbital, lattice and other degrees of freedom can be obtained. Based on an interacting spin wave theory study within the ladder approximation Bethe-Salpeter scheme, we perform a comprehensive analysis of the bimagnon indirect RIXS intensity spectra of the spatially frustrated Jx−Jy−J2 Heisenberg model on a square lattice. We predict the appearance of a two-peak structure over a wide range of transferred momenta in both magnetically ordered phases and the occurrence of RIXS spectrum splitting (instability). We also discuss the signatures of indirect RIXS on a triangular lattice, including a proposal for theexperimental signature to detect rotons in a triangular lattice.

References:
[1] Spectrum splitting of bimagnon excitations in a spatially frustrated Heisenberg antiferromagnet revealed by resonant inelastic x-ray scattering, Phys. Rev. B 89, 165103 (2014) .
[2] Signatures of indirect K-edge resonant inelastic x-ray scattering on magnetic excitations in triangular lattice antiferromagnet, Phys. Rev. B 92, 035109 (2015)