STUDY OF THE CHAIN RELATED FERMI-SURFACE IN (R) BA2CU3O7-DELTA

We have observed, by 2D positron annihilation, the rigid-shaped Fermi surface related to the chains in the compound series (R)Ba2Cu3O7-delta for R = Y, Dy, Ho, and Pr. In the case of Y we have sighted the clear signature of the ridge in the fourth Brillouin zone and have observed the effect of substituting Cu with Ni, Zn, and Al. The presence of th e ridge is also seen in PrBa2Cu3O7-delta which has an insulating chara cter. This shows that chains have a Fermi surface but contribute littl e to conductivity. This observation is discussed in view of the above alloying experiments, and in view of the recent model of Fehren-bacher and Rice.