We report local density approximation plus Hubbard parameter U calculations
of the electronic structure of ABa2Cu3O7 (A=Y, Pr, Nd) including Coulomb
correlations in the f shell. For A=Pr (but not for A=Nd) an additional
band crosses the Fermi level, grabbing holes from the (super)conducting
pd sigma band. On doping Y or Nd with Pr the position of the hole-depleting
band depends on the atomic number of the host rare earth, through the position
of its f level. This makes Tc suppression in doped compounds different
for different hosts the stronger the smaller the atomic number of the host
is, and also explains why an external pressure reduces Tc in doped compounds,
opposite to the effect of the "chemical pressure" (substituting one rare
earth by another with a smaller size).
Physical Review Letters, 74 1000-3, 1995.
Max-Planck Institut für Festkörperforschung;
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