Electronic structure modulations in the stripe phase of La$_{1.475}$Nd$_{0.4}$Sr$_{0.125}$CuO$_4$

A prevailing description of the stripe phase in underdoped cuprate superconductors is that the charge carriers (holes) phase segregate into hole rich regions that form anti-phase boundaries between regions of anti-ferromagnetic order. I will present resonant elastic x-ray scattering measurements of stripe-ordered La$_{1.475}$Nd$_{0.4}$Sr$_{0.125}$CuO$_4$ at the Cu $L_{3,2}$ and O $K$ absorption edges that point to an alternate interpretation of the stripe phase. Analysis of the energy dependence of the scattering intensity reveals that the dominant feature of the charge density wave state is a spatial modulation in the energies of Cu $3d$ and O $2p$ states rather than the large modulation of the valence (charge density) envisioned in the common stripe paradigm. These energy shifts are interpreted as a spatial modulation of the electronic structure, possibly involving a modulation of the Cu $3d$ -- O $2p$ hopping, $t_{pd}$, the onsite Coulomb repulsion, $U_{dd}$, and other local electronic structure parameters. This result may point towards a valence-bond-solid interpretation of the stripe phase, where translational symmetry can be broken with minimal modulation of the charge density.