Nature of Doped Electrons in Nd_2-xCe_xCuO₄: Electronic Band Structures of Nd₂CuO₄Type M₂CuO₄(M=La, Ce and Th)

Abstract

One-electron energy band structures for La 2 CuO 4 , Ce 2 CuO 4 and Th 2 CuO 4 with the Nd 2 CuO 4 type crystal structure were calculated by the self-consistent APW method with the local density approximation. The bonding-antibonding splitting between the Cu 3 d ( x 2 - y 2 ) and O 2 p states on the CuO 2 plane makes a pair of sub-bands. In La 2 CuO 4 , the Fermi energy cuts the middle of antibonding band resulting in the half-filled band. By replacing La with tetravalent Th, the Cu 3 d states raise due to the increase in the number of Cu 3 d electron but the bonding band made from Th 6 d (3 z 2 - r 2 ) state falls down. In Ce 2 CuO 4 , the Fermi energy cuts the bottom of 4 f bands. To raise the 4f states, a correction is introduced to the Ce potential and then Ce becomes nearly tetravalent resulting in similar band structure to that of Th 2 CuO 4 . By considering the strong correlation in the Cu 3 d ( x 2 - y 2 ) state, the doped electrons in Nd 2- x M x CuO 4 (M=Ce, Th) are thought to be injected into the M d (3 z 2 - r 2 ) bonding band.