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Author Bruchhausen, A.; Bahrs, S.; Fleischer, K.; Goni, A.R.; Fainstein, A.; Nieva, G.; Aligia, A.A.; Richter, W.; Thomsen, C. openurl 
  Title Photoinduced chain-oxygen ordering in detwinned YBa2Cu3O6.7 single crystals studied by reflectance-anisotropy spectroscopy Type Journal Article
  Year 2004 Publication PHYSICAL REVIEW B Abbreviated Journal  
  Volume 69 Issue 22 Pages 224508  
  Keywords  
  Abstract 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.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1098-0121 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000222530900070 Approved no  
  Call Number BT @ hernan @ Serial 208  
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Author Bahrs, S.; Bruchhausen, A.; Goni, A.R.; Nieva, G.; Fainstein, A.; Fleischer, K.; Richter, W.; Thomsen, C. openurl 
  Title Effect of light on the reflectance anisotropy and chain-oxygen related Raman signal in untwinned, underdoped crystals of YBa2Cu3O7-delta Type Journal Article
  Year 2006 Publication JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS Abbreviated Journal  
  Volume 67 Issue 1-3 Pages 340-343  
  Keywords  
  Abstract Recent studies of the optical anisotropy of a detwinned, underdoped YBa2Cu3O7-delta-crystal showed that illumination-induced change and recovery in the surface reflectance can be traced on a time scale of hours. This effect of light is also known from Raman bleaching and electrical transport and shares features of the oxygen reordering processes above room temperature. We report temperature-dependent studies of the optical anisotropy using reflectance anisotropy spectroscopy and present time-dependent data for the optical transitions at 2.2 and 4.4 eV. We compare our results to Raman bleaching and discuss them within the picture of superstructure patterns and oxygen-defect reordering in underdoped YBa2Cu3O7-delta. (c) 2005 Elsevier Ltd. All rights reserved.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0022-3697 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:000236746600084 Approved no  
  Call Number BT @ hernan @ Serial 203  
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Author Weiden, M.; Hauptmann, R.; Richter, W.; Geibel, C.; Hellmann, P.; Koppen, M.; Steglich, F.; Fischer, M.; Lemmens, P.; Guntherodt, G.; Krimmel, A.; Nieva, G. openurl 
  Title Magnetic phase diagram of CuGe1-xSixO3 Type Journal Article
  Year 1997 Publication PHYSICAL REVIEW B Abbreviated Journal  
  Volume 55 Issue 22 Pages 15067-15075  
  Keywords  
  Abstract The effect of Si doping on the magnetic properties of the spin-Peierls (SP) system CuGeO3 was found to differ strongly between polycrystals (PC's) and single crystals (SC's). In SC's, the SP state is suppressed much mon strongly, whereas the existence region of the antiferromagnetic (AF) state is enhanced. We investigated the origin of this difference by means of magnetic susceptibility, specific heat, thermal expansion, Raman scattering, elastic neutron scattering, and x-ray measurements on CuGe1-xSixO3 samples prepared under different conditions. The partial oxygen pressure and the temperature during the synthesis were found to have a profound influence on the magnetic properties: preparation under reduced oxygen pressure leads to a stabilization of the AF state, whereas heating above the melting point results in a strong decrease of T-SP in Si-doped samples. Therefore, both the AF stabilization and the TSP reduction observed in SC's are not an intrinsic effect of Si doping PC samples, which can be prepared at lower temperatures and more oxidizing conditions, reflect much better the intrinsic properties of CuGe1-xSixO3. We were able to prepare PC samples up to 50 at. % Si and found a continuous decrease of the one-dimensional character of the magnetic properties without pronounced changes in the structure.  
  Address  
  Corporate Author Thesis  
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  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1098-0121 ISBN Medium  
  Area Expedition Conference  
  Notes ISI:A1997XF60200055 Approved no  
  Call Number BT @ hernan @ Serial 240  
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