We present experimental evidence of the gapless band structure of PbPdO₂ by combined x-ray photoemission and x-ray absorption spectra complemented with first principles band structure calculations. The electronic structure near the Fermi level of PbPdO₂ is mainly composed of O 2p and Pd 4d bands, constructing the conduction path along the Pd-O layer in PbPdO₂. Pd deficiency in PbPdO₂ causes decreased O 2p-Pd 4d and increased O 2p-Pb 6p hybridizations, thereby inducing a small band gap and hence reducing conductivity. Hall measurements indicate that PbPdO₂ is a p-type gapless semiconductor with intrinsic hole carriers transporting in the Pd-O layers. The research was conducted at the NSRRC beamline 20A1. 

S. W. Chen, S. C. Huang, G. Y. Guo, J. M. Lee, S. Chiang, W. C. Chen, Y. C. Liang, K. T. Lu, and J. M. Chen