X-ray dichroism and the pseudogap phase of cuprates

Abstract

A recent polarized x-ray absorption experiment on the high-temperature cuprate superconductor ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+x}$ indicates the presence of broken parity symmetry below the temperature ${T}^{*}$, where a pseudogap appears in photoemission. We critically analyze the x-ray data and conclude that a parity-breaking signal of the kind suggested is unlikely based on the crystal structures reported in the literature. Possible other origins of the observed dichroism signal are discussed. We propose x-ray scattering experiments that can be done in order to determine whether such alternative interpretations are valid or not.