Polarization-dependent angle-resolved photoemission of the layered cuprate Ba2Cu3O4Cl2

We report polarization-dependent angle-resolved photoemission studies of single crystalline Ba₂Cu₃O₄Cl₂. This antiferromagnet adopts a layered body-centered tetragonal structure related to that of the cuprates, but with anextra copper site resulting in a plane with Cu₃O₄ stoichiometry. For the -M direction of the Brillouin zone we observe a dispersive feature with a bandwidth of 400 ±80 meV, which approaches to within 0.9 eV of the Fermi level at (/2,/2). The magnitude of the observed dispersion and its polarization dependence are consistent with its origin as a purely antibonding combination of O2p_x,y and atomic orbitals from the cuprate-like CuO₂ sub-system, i.e. Zhang-Rice singlets.