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.
Highlights
Already in their groundbreaking paper on ‘Possible High Tc Superconductivity in the Ba-La-Cu-O System’ [1] Bednorz and Müller discussed the possibility of ’superconductivity of percolative nature’ to explain their observation
We demonstrate that within a strong coupling expansion the single-band Hubbard model shows an instability towards phase separation and extend the approach for an analysis of phase separation in the Hubbard-Kanamori hamiltonian as a prototypical multiband model
We investigated the mechanism of phase separation in systems with strong electron correlations
Summary
Already in their groundbreaking paper on ‘Possible High Tc Superconductivity in the Ba-La-Cu-O System’ [1] Bednorz and Müller discussed the possibility of ’superconductivity of percolative nature’ to explain their observation. It was proposed [14,21,22] that the inclusion of long-range Coulomb interactions is a crucial ingredient since they suppress long-wavelength charge density fluctuations associated with phase separation favoring shorter-wavelength density fluctuations, giving rise either to dynamical slow density modes [14] or to incommensurate charge density waves [22] Such incommensurate structures have been observed in La1.48Nd0.4Sr0.12CuO4 by Tranquada and collaborators who detected a splitting of both spin and charge order peaks by elastic neutron scattering experiments [23]. For this purpose we first review the pairing mechanism due to long-range optical phonon modes as proposed by Hizhnyakov and Sigmund [56,57,58]. We exemplify the isotropy of superconducting correlations for a striped system where it turns out that for both d- and extended s-wave symmetry the corresponding vertex contribution has only a marginal orientational dependence
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