Photoinduced chain-oxygen ordering in detwinned YBa2Cu3O6.7 single crystals studied by reflectance-anisotropy spectroscopy

BRUCHHAUSEN, A; BAHRS, S; FLEISCHER, K; GONI, AR; FAINSTEIN, A; NIEVA, G; ALIGIA, AA; RICHTER, W; THOMSEN, C

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

Año: 2004 vol. 69 p. 2245081 - 2245085

0163-1829

We present a reflectance-anisotropy spectroscopy (RAS) investigation of photoexcitation and annealing effects in oxygen deficient detwinned YBa2Cu3O6.7 single crystals. Well-resolved RAS spectral features are either bleached or enhanced on a time scale of hours upon laser illumination with polarization parallel to the Cu(1)-O(1) chains. These photoinduced effects recover with room temperature annealing in the dark. Based on previous ellipsometric studies and on cluster models for the oxygen Cu-O(1) chain-fragments we are able to assign the RAS peaks that depend on illumination to optical transitions involving copper atoms located either on short chain-fragments or in isolated Cu-O(4)(2) sites. This provides strong evidence that photoinduced chain-oxygen ordering is indeed at the origin of persistent photoconductivity and Raman vibrational mode bleaching in these materials.