O-17 NMR IN YBA2CU3O6.65 DISCRIMINATION BETWEEN T-J AND 2-BAND MODELS - A NEW APPROACH

17O NMR has been performed between 10 and 360 K on an oriented powder of YBa2Cu3O6.65 (Tc=60 K). The temperature dependence of the magnetic hyperfine shift (MHS) tensors has been followed for the O(2,3) and O(4) sites. For O(4) nuclei, the MHS stays constant above Tc, whereas for the O(2,3) sites it scales linearly with the macroscopic susceptibility χm. This demonstrates that the origin of the temperature dependence of χm is to be found within the CuO2 plane. Two methods are presented to discriminate between the t-J model and two-band models: (a) the comparison of the temperature dependence of the isotropic Kiso and the axial part Kax of the O(2,3) MHS, (b) a scaling between the experimentally measured products K2 iso T1T in 17O and 89Y. From the second method, our results indicate the existence of an oxygen 2p-band with a density of states per spin direction of 0.11 to 0.19 eV-1 at-1. © 1990.