Аннотации:
Using the model of the singlet-correlated band, the temperature and doping dependences of the planar Cu Knight shift in YBa2Cu3O7 and YBa2Cu4O8, at T > Tc, have been calculated. The spin susceptibility has been deduced by means of a Hubbard-like theory in the fast fluctuating regime. The effect of strong correlation shows up as an additional correction to the Pauli susceptibility with a strong dependence on the doping level.