The anomalous momentum and doping dependence of the electron spectral function and electron dispersion for copper oxide materials in the underdoped regime are studied within the t-J model. It is shown that the electron spectrum is changed with dopings, and the electron dispersion exhibits a flat band around ($\pi$,0) point in the Brillouin zone, which leads to the normal-state pseudogap formation. The theoretical results are consistent with the experiments and numerical simulations.
Categories: cond-mat.str-el cond-mat.supr-con