Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 8: Correlated Electrons: Spin Systems and Itinerant Magnets - Frustrated Magnets I

TT 8.9: Talk

Monday, March 31, 2014, 11:45–12:00, HSZ 304

Band structure and optical properties of Na₃Ir₃O₈ — •Alexander Yaresko — MPI FKF, Stuttgart, Germany

Na₄Ir₃O₈ attracted much attention due to its fascinating magnetic properties. It is a weak Mott insulator in which magnetic Ir⁴⁺ ions form a frustrated non-centrosymmetric hyper-kagome lattice. Because of geometrical frustrations Ir spins do not order down to lowest temperature but instead remain in a 3D spin-liquid state. Recently, monocrystals of another hyper-kagome Ir compound Na₃Ir₃O₈ have been synthesized, In contrast to Na₄Ir₃O₈, Na₃Ir₃O₈ is a semi-metal with a low carrier density and weak paramagnetism of valence electrons. If spin-orbit interaction (SOI) is neglected, LDA calculations for Na₃Ir₃O₈ give an insulating solution despite of noninteger Ir^4.33+ valence. SOI, however, closes the band gap and Na₃Ir₃O₈ becomes a compensated metal. In this presentation it is shown that the gap appears because of formation of quasi-molecular orbitals on Ir triangles which become partially delocalized due to SOI. The semi-metallic band structure together with the lack of inversion symmetry lead to unusual optical properties which seem to suggest anomalously strong electron-phonon coupling.