Resonating valence bond localization by impurities in high temperature superconductors, observed by Mo¨ssbauer spectroscopy

Abstract The temperature dependence of the Mo¨ssbauer spctra of 0.12 weight % 57 Fe enriched up % in the high T c -superconductor Y 1 Ba 2 Cu 3 O 7−δ is studied. The intensity of one quadrapole doublet appears to be strongly temperature dependent and decreases dramatically in the superconducting state. Arguments for liberation of the localized valence bonds around the Fe-impurities in the Cu(1) sites are presented.