Phase separation and pairing fluctuations in oxide materials

TL;DR

This paper explores the microscopic mechanisms behind charge instabilities, phase separation, and pairing fluctuations in strongly correlated oxide materials, shedding light on the coexistence of stripe order and d-wave superconductivity in cuprates.

Contribution

It extends the strong coupling expansion approach to analyze phase separation in multiband Hubbard models and examines pairing fluctuations on inhomogeneous stripe states.

Findings

Hubbard model shows an instability towards phase separation.

d-wave pairing fluctuations are prominent in the active subband crossing the Fermi level.

Low energy spin and charge fluctuations can transfer d-wave correlations to quasiparticle bands.

Abstract

We investigate the microscopic mechanism of charge instabilities and the formation of inhomogeneous states in systems with strong electron correlations. It is demonstrated 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.