Seminar TRR80

17.10.2017 4 p.m., room: S-288
Prof. Dr. Arthur Ernst (Johannes Kepler Universität Linz, Österreich)
Exchange interaction in magnetic topological insulators and related materials
21.11.2017 4 p.m., room: S-288
Dr. Axel Lubk (IFW Dresden)
Advanced Holographic Tomography for 3D Magnetic Imaging in Magnetic Textures
5.12.2017 4 p.m., room: S-288
Prof. Dr. Martino Poggio (Department of Physics, University of Basel)
Nanomechanics and Nanomagnetism
16.1.2018 4 p.m., room: S-288
Prof. Dr. Markus Grüninger (II. Physikalisches Institut, Universität zu Köln)
RIXS on face-sharing iridates: From j=1/2 to quasi-molecular orbitals

Spin-orbit entangled j=1/2 Mott insulators set the stage for fascinating novel quantum states of matter. In corner-sharing geometry of the IrO6 octahedra, one finds strong Heisenberg exchange between j=1/2 moments, while edge-sharing geometry features bond-directional Kitaev exchange. The case of face-sharing octahedra has hardly been explored. Using resonant inelastic x-ray scattering (RIXS), we study Ba3MIr2O9 with face-sharing octahedra forming triangular layers. Both spin-orbit coupling and hopping are large within the bioctahedra. For M=Ce4+ with Ir 5d5 configuration, the RIXS data reveal the first and exceptionally clean realization of the quasi-molecular-orbital scenario that was debated extensively (but refuted) for Na2IrO3. The ground state shows a total j=0 singlet predominantly built from j=1/2 moments with the corresponding triplet excitation lying at an extraordinarily large energy. In 5d5 Ba3Ti(3-x)Ir(x)O9 with Ti/Ir site disorder, we observe a coexistence of quasi-molecular singlets and j=1/2 moments, explaining the unusual behaviour of the magnetic susceptibility. Finally, we establish a quasi-molecular-orbital character of the electronic states in the putative spin liquid Ba3InIr2O9 with mixed-valence Ir+4.5 ions.