Photoemission resonances of the high-temperature superconductor ${\mathrm{Ba}}_2$${\mathrm{YCu}}_3$${\mathrm{O}}_{7+\mathrm{x}}$

We studied photoemission resonances in the spectra of ${\mathrm{Ba}}_2$ ${\mathrm{YCu}}_3$ ${\mathrm{O}}_{7+\mathrm{x}}$. From these, and in general from the photon-energy dependence of the partial photoionization cross sections, we identify different contributions to the electronic structure in the region 0–22 eV below the Fermi level. Careful studies as a function of temperature did not reveal changes in the spectral region close to the Fermi level across the phase transition. The significance of this result in light of the possible superconductivity models is discussed.