Photoemission spectroscopy study of the hole-doped Haldane chain Y2-xSrxBaNiO5

In this paper, we present photoemission experiments on the hole-doped\r\n Haldane chain compound Y2-xSrxBaNiO5. By using the photon energy\r\n dependence of the photoemission cross section, we identified the\r\n symmetry of the first ionisation states (d type). Hole doping in this\r\n system leads to a significant increase in the spectral weight at the top\r\n of the valence band without any change in the vicinity of the Fermi\r\n energy. This behavior, never observed in other charge transfer oxides,\r\n could result from the Ni-3d-O-2P hybridization enhancement due to the\r\n shortening of the relevant Ni-O distance with doping. (C) 2002 Elsevier\r\n Science B.V. All rights reserved.