Asymmetry in band widening and quasiparticle lifetimes in SrVO₃: Competition between screened exchange and local correlations from combined GW and dynamical mean-field theory GW + DMFT

Abstract

The very first dynamical implementation of the combined GW and dynamical mean-field scheme "GW + DMFT" for a real material was achieved recently [Tomczak et al., Europhys. Lett. 100, 67001 (2012)], and applied to the ternary transition metal oxide SrVO3. Here, we review and extend that work, giving not only a detailed account of full GW + DMFT calculations, but also discussing and testing simplified approximate schemes. We give insights into the nature of exchange and correlation effects: dynamical renormalizations in the Fermi liquid regime of SrVO3 are essentially local, and nonlocal correlations mainly act to screen the Fock exchange term. The latter substantially widens the quasiparticle band structure, while the band narrowing induced by the former is accompanied by a spectral weight transfer to higher energies. Most interestingly, the exchange broadening is more pronounced in the unoccupied part of the spectrum than in the occupied one. In addition, shorter lifetimes for unoccupied states further contribute to making the corrections to the Kohn-Sham band structure asymmetric with respect to the chemical potential. As a result, the GW + DMFT electronic structure of SrVO3 resembles the conventional density functional based dynamical mean-field (DFT + DMFT) description for occupied states but is profoundly modified in the empty part. Our work leads to a reinterpretation of inverse photoemission spectroscopy (IPES) data. Indeed, we assign a prominent peak at about 2.7 eV dominantly to eg states, rather than to an upper Hubbard band of t2g character. Similar surprises can be expected for other transition metal oxides. This prediction urgently calls for more detailed investigations of conduction band states in correlated materials.