Normal‐state 63Cu Knight shift and hole‐band modification in Y1−xPrxBa2Cu3O7

The 63Cu NMR Knight shift K has been measured in oriented powder samples of normal‐state Y1−xPrxBa2Cu3O7, x=0.2 and 0.4. At plane Cu sites K is found to decrease with Pr doping, and a temperature dependence (dK/dT>0) develops. The variation of K with bulk susceptibility χ is considerably greater than can be explained using RKKY coupling between Pr spins and Cu nuclei, and the temperature variation of K resembles that of χ in high‐Tc systems with reduced conduction‐hole concentration. These results are consistent with the view that Pr impurities significantly modify conduction‐band properties, rather than acting as a ‘‘conventional’’ pair‐breaking mechanism.