Transport properties and fluctuations in underdoped GdBa2Cu3Ox thin films

We have investigated the transport properties, resistivity and Hall effect, in a series of underdoped GdBa2Cu3Ox thin films grown by off-axis magnetro n sputtering. We find a systematic correlation between the critical tempera ture T-c and the inverse Hall constant R-H(-1), related, in simple models, to the carrier concentration n. Our experimental thin film T-c(n) data are in good agreement with the temperature-doping phase diagram obtained for YB a2Cu3Ox, single crystals. By measuring the activation energies in the liqui d vortex phase, and by using a 2-dimensional model for vortex dynamics, we have extracted the penetration depth of these samples, and studied the rela tion between the carrier concentration and the superfluid density to probe the role of phase fluctuations on superconductivity. PACS numbers: 74.25 Dw , 74,25 Fy, 74.76 Bz.