Nonlocal electron-phonon interaction as a source of dynamic charge stripes in the cuprates

Abstract

We calculate for La2CuO4 the phonon-induced redistribution of the electronic charge density in the insulating, the underdoped pseudogap and the more conventional metallic state as obtained for optimal and overdoping, respectively. The investigation is performed for the anomalous high-frequency-oxygen-bond stretching modes (OBSM) which experimentally are known to display a strong softening of the frequencies upon doping in the cuprates. This most likely generic anomalous behaviour of the OBSM has been shown to be due to a strong nonlocal electron-phonon interaction (EPI) mediated by charge fluctuations on the ions. The modeling of the competing electronic states of the cuprates is achieved in terms of consecutive orbital selective incompressibility-compressibility transitions for the charge response. We demonstrate that the softening of the OBSM in these states is due to nonlocally induced dynamic charge inhomogenities in form of charge stripes along the CuO bonds with different orbital character. Thus, a multi-orbital approach is essential for the CuO plane. The dynamic charge inhomogeneities may in turn be considered as precursors of static charge stripe order as recently observed in La$_{2-x}$Ba$_{x}$CuO$_{4}$ in a broad range of doping around x=1/8. The latter may trigger a reconstruction of the Fermi surface into small pockets with reduced doping. We argue that the incompressibility of the Cu3d orbital and simultaneously the compressibility of the O2p orbital in the pseudogap state seems to be required to nucleate dynamic stripes.