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TT: Fachverband Tiefe Temperaturen

TT 72: Poster Session: Correlated Electrons

TT 72.25: Poster

Mittwoch, 14. März 2018, 15:00–19:00, Poster B

RIXS on 5d⁵ Ba₃CeIr₂O₉ and Ba₃Ti_xIr_3−xO₉ — •Alessandro Revelli¹, Marco Moretti Sala², Giulio Monaco³, Petra Becker⁴, Ladislav Bohatý⁴, Thomas Koethe¹, Tobias Fröhlich¹, Maria Hermanns⁵, Paul H.M. van Loosdrecht¹, Jeroen van den Brink⁶, and Markus Grüninger¹ — ¹II. Physikalisches Institut, Universität zu Köln — ²ESRF, Grenoble — ³Dipart. di Fisica, Universita di Trento — ⁴Abt. Kristallographie, Institut für Geologie & Mineralogie, Universität zu Köln — ⁵Institut für Theoretische Physik, Universität zu Köln — ⁶IFW, Dresden

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. However, the case of face-sharing octahedra has hardly been explored. Using resonant inelastic x-ray scattering (RIXS), we study the 5d⁵ compound Ba₃CeIr₂O₉ with face-sharing octahedra forming triangular layers. Both hopping and spin-orbit coupling are large. 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. For M=Ti, the compound Ba₃Ti_xIr_3−xO₉ exists for different values of x and shows Ti/Ir site disorder. In RIXS we observe a coexistence of j = 1/2 moments and quasi-molecular singlets.