Photoemission study of single-crystal ${\mathrm{Bi}}_2$${\mathrm{Sr}}_{1.9}$${\mathrm{Pr}}_{0.1}$${\mathrm{CuO}}_{6+\mathrm{\delta }}$

We performed exploratory angle-integrated and angle-resolved photoemission-spectroscopy measurements on Pr-stabilized single crystals of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_6$ (${\mathit{T}}_{\mathit{c}}$∼10 K). Fermi-level crossings along principal directions match some crossings predicted by tight-binding calculations. These crossings differ from both the Fermi-surface mapping and the local-density-approximation-derived Fermi surfaces on the much studied ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_1$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ (${\mathit{T}}_{\mathit{c}}$∼75–96 K). We observe optical-polarization effects in the angle-resolved spectra, which is consistent with the states near ${\mathit{E}}_{\mathit{F}}$ being derived from the orbitals containing ${\mathit{d}}_{\mathit{x}}^2$-${\mathit{y}}^2$ symmetry. The density-of-states contribution from the Pr 4f states derived by resonant-photoemission spectroscopy suggests that the Pr 4f states do not hybridize strongly and lie away from the Fermi level, thus not affecting the superconductivity of the Bi-Sr-Ca-Cu-O system.