Electronic structure of correlated solid-state systems by ab initio wavefunction-based methods

• Applicant: Dr. Liviu Hozoi
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: from 2010 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 163359453

• Final Report Year: 2014

Final Report Abstract

This project was concerned with the theoretical investigation of the electronic structure of intriguing materials of major present (scientific and technological) interest. Representative systems were here the parent compounds of the copper oxide high­temperature superconductors and the strongly spin­orbit coupled iridium oxides. The discovery of the former brought hope for large­scale applications of superconducting devices functioning above the boiling point of liquid nitrogen. The latter, e.g., the honeycomb­lattice iridates Na2IrO3 and Li2IrO3, are being intensively studied as a potential experimental realization of the Kitaev spin model, of particular relevance in the context of quantum computing. First­principles methods from wavefunction­based theoretical chemistry were employed for our theoretical and computational endeavor. A main issue was the study of the essential trends along the series of both two­dimensional and one­dimensional 3d9 cuprates as concerns the 3d­level energy order and splittings. The latter determine the precise shape of the Fermi surfaces in the doped systems and are therefore believed to crucially influence properties such as the value of the critical temperature. On the experimental side, a main investigation tool is here resonant inelastic x­ray spectroscopy (RIXS) and the quantum chemistry calculations constitute a reliable way of helping with the interpretation of the RIXS spectra. This is the reason close collaborations were set up with RIXS experimental groups in Milano, Villigen, Toronto, Brookhaven, Taiwan, and Stuttgart. Attention has been also given to the electronic structure and magnetic interactions in Fe 3d6 pnictide superconductors. Further, we have been carrying out extensive investigations on the interplay between electron correlation effects and spin­orbit couplings in 5d oxides. This is a largely unexplored territory but new and striking physical effects have been recently predicted and in some cases confirmed. The Ir 5d5 oxides, in particular, are being intensively studied as candidates for the experimental realization of spin­orbital jeff=1/2 Mott­like ground states, high­temperature superconductivity as in the 3d9 cuprates, or exotic topological states. Our ab initio computational work provided much needed insight into the detailed electronic structure of these systems, in particular, when and why the jeff=1/2 picture is (or not) appropriate and what is the magnitude of the magnetic intersite couplings in various iridates. Given the unprecedented accuracy achieved for the computation of the d­d valence excitations in both copper and iridium oxides, intensive work is now being carried out by our team in Dresden for the calculation of full RIXS spectra, having the core­hole intermediate states and the valence­shell relaxation in the presence of the core­level hole explicitly accounted for. The investigation of magnetic couplings in 5d oxides is at the origin of our present work on highly anisotropic superexchange interactions in a wide variety of 5d 5 iridates. Some of these later studies are now completed, e.g., the reliable computation of Kitaev exchange constants the in honeycomb­lattice materials Na2IrO3 and Li2IrO3.

Publications

• Ab initio calculation of d­d excitations in quasi­1D Cu d9 correlated materials, Physical Review B 84, 235125 (2011)
  H.­Y. Huang, N. A. Bogdanov, L. Siurakshina, P. Fulde, J. van den Brink, and L. Hozoi
  
• Ab initio determination of Cu 3d orbital energies in layered copper oxides, Nature Scientific Reports 1, 65 (2011)
  L. Hozoi, L. Siurakshina, P. Fulde, and J. van den Brink
  
• Spin­orbital separation in the quasi­one­dimensional Mott insulator Sr2CuO3, Nature 485, 82 (2012)
  J. Schlappa, K. Wohlfeld, K. J. Zhou, M. Mourigal, M. W. Haverkort, V. N. Strocov, L. Hozoi, C. Monney, S. Nishimoto, S. Singh, A. Revcolevschi, J.­S. Caux, L. Patthey, H. M. Rønnow, J. van den Brink, and T. Schmitt
  (See online at https://doi.org/10.1038/nature10974)
• Magnetic State of Pyrochlore Cd2Os2O7 Emerging from Strong Competition of Ligand Distortions and Longer­Range Crystalline Anisotropy, Physical Review Letters 110, 127206 (2013)
  N. A. Bogdanov, R. Maurice, I. Rousochatzakis, J. van den Brink, and L. Hozoi
  (See online at https://doi.org/10.1103/PhysRevLett.110.127206)
• Measurement of the effect of lattice strain on magnetic interactions and orbital splitting in CaCuO2 using resonant inelastic x­ray scattering, Physical Review B 87, 085124 (2013)
  M. Minola, L. Hozoi, D. Di Castro, R. Felici, M. Moretti Sala, A. Tebano, G. Balestrino, G. Ghiringhelli, J. van den Brink, and L. Braicovich
  (See online at https://doi.org/10.1103/PhysRevB.87.085124)
• Tuning Magnetic Coupling in Sr2IrO4 Thin Films with Epitaxial Strain, Physical Review Letters 112, 147201 (2014)
  A. Lupascu, J. P. Clancy, H. Gretarsson, Z. Nie, J. Nichols, J. Terzic, G. Cao, S. Seo, Z. Islam, M. H. Upton, J. Kim, A. H. Said, D. Casa, T. Gog, V. M. Katukuri, H. Stoll, L. Hozoi, J. van den Brink, and Y. J. Kim
  (See online at https://doi.org/10.1103/PhysRevLett.112.147201)