Microwave surface impedance of Nd-rich Nd1-xBa2-xCu3O7-delta thin films

Surface impedance measurements on highly c-axis epitaxial Nd1+xBa2-xCu3O7 (x = 0, 0.09 and 0.12) films grown by d.c. magnetron sputtering on LaAlO3 substrates are presented. It is found that the zero temperature London penetration depth correlates well with the critical temperature of the films and with the corresponding number of carriers. The low temperature penetration depth follows a linear T law for optimally doped Nd123 sample and a T^2 law in Nd-rich samples. In the case of the heavily underdoped samples (T-c < 60K) the T^2 law extends to temperatures higher than Tc/2. The possible role of the Nd/Ba ions substitution on the penetration depth and surface resistance is discussed.