@misc{BillHizhnyakovKremeretal., author = {Bill, Andreas and Hizhnyakov, Vladimir and Kremer, Reinhard K. and Seibold, G{\"o}tz and Shelkan, Aleksander and Sherman, Aleksei}, title = {Phase Separation and Pairing Fluctuations in Oxide Materials}, series = {Condensed Matter}, volume = {5}, journal = {Condensed Matter}, number = {4}, issn = {2410-3896}, doi = {10.3390/condmat5040065}, pages = {23}, abstract = {The microscopic mechanism of charge instabilities and the formation of inhomogeneous states in systems with strong electron correlations is investigated. We demonstrate that within a strong coupling expansion the single-band Hubbard model shows an instability towards phase separation and extend the approach also for an analysis of phase separation in the Hubbard-Kanamori hamiltonian as a prototypical multiband model. We study the pairing fluctuations on top of an inhomogeneous stripe state where superconducting correlations in the extended s-wave and d-wave channels correspond to (anti)bound states in the two-particle spectra. Whereas extended s-wave fluctuations are relevant on the scale of the local interaction parameter U, we find that d-wave fluctuations are pronounced in the energy range of the active subband which crosses the Fermi level. As a result, low energy spin and charge fluctuations can transfer the d-wave correlations from the bound states to the low energy quasiparticle bands. Our investigations therefore help to understand the coexistence of stripe correlations and d-wave superconductivity in cuprates.}, language = {en} } @inproceedings{ShelkanSigmundHizhnyakovetal., author = {Shelkan, Aleksander and Sigmund, Ernst and Hizhnyakov, Vladimir and Seibold, G{\"o}tz}, title = {Free and spin-polaron states in high-Tc superconductor}, series = {Proceedings of the NATO Advanced Research Workshop on Colossal Magnetoresistance and Vibronic Interactions and the XVth International Jahn-Teller Symposium on Vibronic Interactions in Crystals and Molecules, Boston, August 16 - 22, 2000}, booktitle = {Proceedings of the NATO Advanced Research Workshop on Colossal Magnetoresistance and Vibronic Interactions and the XVth International Jahn-Teller Symposium on Vibronic Interactions in Crystals and Molecules, Boston, August 16 - 22, 2000}, editor = {Kaplan, Michael D.}, publisher = {Kluwer}, address = {Dordrecht [u.a.]}, isbn = {1-402-00044-8}, pages = {349 -- 356}, language = {en} }