Effect of light on the reflectance anisotropy and chain-oxygen related Raman signal in untwinned, underdoped crystals of YBa_2Cu_3O_{7-\delta}

S. BAHRS; A. BRUCHHAUSEN; A. R. GOÑI; G. NIEVA; A. FAINSTEIN; K. FLEISCHER; C. THOMSEN

Sitges, Spain

Conferencia; 7th International Conference on Spectroscopies in Novel Superconductors (SNS2004); 2004

Recent studies of the optical anisotropy of a detwinned, underdoped YBa_2Cu_3O_{7-delta}$ -crystal showed that illumination-induced change and recovery in the surface reflectance can be traced on a time scale of hours.[1] This kind of interaction with light is known from other effects in the material such as Raman bleaching and electrical transport and shares features of the oxygen reordering processes above room temperature.[2,3,4] We report a detailed temperature dependence study of photoexcitation efects in the optical anisotropy using Reflectance Anisotropy Spectroscopy. Time dependent data is presented for the optical transitions at 2.2, 4.1 and 4.5 eV. Our results on illumination induced change in the reflectance anisotropy are compared to the time and temperature dependence of the Raman signal.[5,6] Both signals can be bleached by illumination through an additional laser with polarization parallel to the chain direction and both signals can be temperature-cycled: the signals recover from the light-induced bleaching when warmed up to room temperature. We discuss the connection between these two processes in terms of the oxygen reordering model. [1]. A. Bruchhausen et al., Phys. Rev. B, submitted.[2]. D. R. Wake et al., Phys. Rev. Lett. 67, (1991) 3728.[3]. G. Nieva. et al., App. Phys. Lett. 60, (1992) 2159.[4]. J. D. Jorgensen et al., Physica C 167, (1990) 571.[5]. S. Bahrs et al., Phys. Rev. B 65 (2002) 024522.[6]. S. Bahrs et al., Phys. Rev. B, submitted.