Effect of a temperature dependent effective quasiparticle mass on the surface impedance of YBa2Cu3O7-x A. Cassinese, M. A. Hein, S. Hensen and G. Müller Eur. Phys. J. B, 14 4 (2000) 605-610 Published online: 15 April 2000 DOI: 10.1007/s100510051068