Colloquium: "Magnetic Frustrations and Lattice Anisotropy Effects on Indirect RIXS Spectra of Heisenberg Magnets"Thursday, March 23, 2017 - 16:00 to 17:15
Dr. Trinanjan Datta
Associate Professor of Physics
Department of Chemistry and Physics
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 the interacting spin wave theory study within the ladder approximation Bethe-Salpeter scheme, we perform a comprehensive analysis of the K-edge bimagnon indirect RIXS intensity spectrum 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 (Neel- and collinear antiferromagnetic phase) and the occurrence of RIXS spectrum splitting (instability). We also discuss the signatures of bimagnon and trimagnon excitations in the indirect K-edge RIXS spectrum of a triangular lattice quantum magnet.