Electronic structures of high‐ T c superconductors LnBa 2 Cu 3 O 7 (Ln  Pr, Nd, Gd, Dy)

In the present paper, the electronic energy‐band structures of the LnBa 2 Cu 3 O 7 (Ln = Pr, Nd, Gd, and Dy) were investigated employing the EHMO approach based on the tight‐binding method. The results show that the substitution of Nd, Gd, and Dy for Y in YBa 2 Cu 3 O 7 complicates the shape of the Fermi surface and results in an increase in the number of energy bands crossing the Fermi level, Ef . Compared with those of YBa 2 Cu 3 O 7 , the electronic densities of states at Ef, N(Ef) , for NdBa 2 Cu 3 O 7 , GdBa 2 Cu 3 O 7 , and DyBa 2 Cu 3 O 7 increase greatly, whereas those of PrBa 2 Cu 3 O 7 are very small. The results given by the present calculations explain why the substitution of Nd, Gd, and Dy for Y in YBa 2 Cu 3 O 7 can still maintain the high transition temperature T c , while PrBa 2 Cu 3 O 7 is a semiconductor rather than a superconductor. © 1993 John Wiley & Sons, Inc.