Optical study of RE1+xBa2-xCu3O6 (RE = Nd, Sm) and YBa2Cu3O6 in the mid infrared range D. Barba, S. Jandl, A. A. Martin, C. T. Lin, M. Cardona and T. Wolf Eur. Phys. J. B, 22 3 (2001) 277-281 Published online: 15 August 2001 DOI: 10.1007/PL00011148