Angle-resolved photoemission spectra of single-crystal ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathrm{x}}$

Angle-resolved photoemission measurements have been made on the recently discovered high-$T_c$ superconductor ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathrm{x}}$. From the results, E vs $k_{?}$ dispersion curves have been obtained along two principal symmetry directions in the two-dimensional Brillouin zone. Compared to results of one-electron band calculations, the observed bands are shifted and distorted by strong correlation effects. One band intersects the Fermi level. This band is assigned to the renormalized ‘‘heavy-electron’’ band.