Nonlocal Electron-Phonon Interaction as a Source of Dynamic Charge Stripes in the Cuprates

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, which experimentally are known to display a strong softening of the frequencies upon doping in the cuprates. This most likely generic anomalous behaviour of these modes is shown to be due to a strong nonlocal electron-phonon interaction mediated by charge fluctuations on the ions. We demonstrate that the softening of the modes is caused by nonlocally induced dynamic charge inhomogeneities in form of charge stripes along the CuO bonds with different orbital character. The dynamic charge inhomogeneities may in turn be considered as precursors of static charge stripe order as recently observed in in a broad range of doping around . The latter may trigger a reconstruction of the Fermi surface into small pockets with reduced doping. We argue that the incompressibility of the orbital and simultaneously the compressibility of the orbital in the pseudogap state seem to be required to nucleate dynamic stripes.