Multiorbital Nature of Doped Sr2IrO4

The low-energy jeff = 1/2 band of Sr2IrO4 bears stark resemblances with the x2 - y2 band of La2CuO4, and yet no superconductivity has been found so far by doping Sr2IrO4. Behind such a behavior could be inherent failures of the jeff = 1/2 picture, in particular when electrons or holes are introduced in the IrO2 planes. In view of this, here we reanalyze the jeff = 1/2 scenario. By using the local-density approximation plus dynamical mean-field theory approach, we show that the form of the effective jeff = 1/2 state is surprisingly stable upon doping. This supports the jeff = 1/2 picture. We show that, nevertheless, Sr2IrO4 remains in essence a multiorbital system: The hybridization with the jeff = 3/2 orbitals sizably reduces the Mott gap by enhancing orbital degeneracy, and part of the holes go into the jeff = 3/2 channels. These effects cannot be reproduced by a simple effective screened Coulomb repulsion. In the optical conductivity spectra, multiorbital processes involving the jeff = 3/2 states contribute both to the Drude peak and to relatively low-energy features.