We study the electronic structure within a system of phase-decoupled one-dimensional superconductors coexisting with stripe spin and charge density wave order. This system has a nodal Fermi surface (Fermi arc) in the form of a hole pocket and an anti
nodal pseudogap. The spectral function in the antinodes is approximately particle-hole symmetric contrary to the gapped regions just outside the pocket. We find that states at the Fermi energy are extended whereas states near the pseudogap energy have localization lengths as short as the inter-stripe spacing. We consider pairing which has either local d-wave or s-wave symmetry and find similar results in both cases, consistent with the pseudogap being an effect of local pair correlations. We suggest that this state is a stripe ordered caricature of the pseudogap phase in underdoped cuprates with coexisting spin-, charge-, and pair-density wave correlations. Lastly, we also model a superconducting state which 1) evolves smoothly from the pseudogap state, 2) has a signature subgap peak in the density of states, and 3) has the coherent pair density concentrated to the nodal region.
We present Raman measurements on the iron-pnictide superconductors CeFeAsO_{1-x}F_{x} and NdFeAsO{1-x}F_{x}. Modeling the Fe-As plane in terms of harmonic and a cubic anharmonic Fe-As interaction we calculate the temperature dependence of the energy
and lifetime of the Raman active Fe B_{1g} mode and fit to the observed energy shift. The shifts and lifetimes are in good agreement with those measured also in other Raman studies which demonstrate that the phonon spectrum is well represented by phonon-phonon interactions without any significant electronic contribution. We also estimate the anharmonic expansion from Fe (56->54) isotope substitution to Delta a=5.1 10^{-4}AA and Delta d_{Fe-As}= 2.510^{-4}AA and the shift of harmonic zero point fluctuations of bond lengths <Delta x^2><=3 10^{-5}AA^2, giving a total relative average decrease of electronic hopping integrals of |delta t|/t<= 2.0 10^{-4}. The results poses a serious challenge for any theory of superconductivity in the pnictides that does not include electron-phonon interactions to produce a sizable Fe-isotope effect.
For a doped antiferromagnet with short-range spin stripe correlations and long-range charge stripe order we find that the manifestation of charge order changes abruptly as a function of momentum along the Fermi surface. The disorder averaged local de
nsity of states is almost perfectly homogeneous when integrated only over states which contribute to the ``nodal spectral weight whereas it displays long range charge stripe order when integrated only over states which contribute to the ``antinodal spectral weight. An effectively two dimensional nodal liquid can thus coexist with static charge stripes provided there is no static spin order. We also study commensurate spin and charge stripe ordered systems where the Fermi surface consists of a nodal hole pocket and an open ``stripe band section. Due to the stripe order the relation between hole density and size of a pocket will be reduced compared to a paramagnet by a factor of two for even charge period and four for odd charge period and we find an estimated upper limit on the area fraction of a hole pocket of 1.6% for charge period four and 4% for charge period five. We also discuss why electron pockets are not expected for a stripe ordered system and show that the open Fermi surface section may be electron like with a negative Hall coefficient.
