A strong paramagnetic resonance signal characteristic of Cu2+ ions in ‖x2-y2〉 states is observed in the high-Tc≊90 K superconductor Y0.2Ba0.8CuOx. The line intensity of the ioniclike signal shows a deviation from Curie behavior at T≳Tc. It is speculated that the phase that is responsible for the signal is an example of an Anderson lattice with an unusually high Kondo temperature.
Mehran, F.; Barnes, S. E.; McGuire, T. R.; Gallagher, W. J.; Sandstrom, R. L.; Dinger, T. R.; and Chance, D. A., "Paramagnetic Resonance of Cu2+ Ions in the Superconductor Y0.2Ba0.8CuOx" (1987). Physics Articles and Papers. 59.