We have performed an angle resolved photoemission spectroscopy (ARPES) study of lightly-doped to underdoped YBa2Cu3Oy (YBCO) untwinned single crystals and a core-level x-ray photoemission spectroscopy (XPS) study of YBCO single and polycrystals. In the zone diagonal (nodal) direction, dispersive quasi-particle (QP) features crossing the Fermi level were observed down to the hole concentration of ~ 4%, which explains the metallic transport of the lightly-doped YBCO. The chemical potential shift estimated from XPS was more rapid than in the Bi2212 cuprates. Upon hole doping, very rapid spectral weight transfer from high binding energies to the QP feature, even faster than La2-xSrxCuO4, was observed.
@article{arxiv.1002.0655,
title = {Characteristic electronic structure and its doping evolution in lightly-doped to underdoped YBa2Cu3Oy},
author = {H. Yagi and T. Yoshida and A. Fujimori and K. Tanaka and N. Mannella and W. L. Yang and X. J. Zhou and D. H. Lu and Z. -X. Shen and Z. Hussain and M. Kubota and K. Ono and K. Segawa and Y. Ando and D. Iijima and M. Goto and K. M. Kojima and S. Uchida},
journal= {arXiv preprint arXiv:1002.0655},
year = {2010}
}