Transport properties and pseudogap in NdBa2-xLaxCu3O7-δ superconductors

Polycrystalline samples of NdBa2-xLaxCu3O7-δ with x=0, 0.05, 0.10, 0.15, 0.20, and 0.30 were made by standard solid state methods. The transport and superconducting properties have been studied by the resistivity measurements as a function of temperature and doping concentration. In order to measurements the hole concentration in CuO2 planes, the room temperature thermoelectric power was measured as a function of La doping. The resistance and the room temperature thermoelectric power were increased while the critical temperature was decreased as parabolic-like by increasing doping concentration. The pseudogap temperature (or pseudogap energy) was measured from downturn deviation in a linear dependence of resistance as a function of temperature. The critical temperature, room temperature thermoelectric power S(290 K), resitivity, and pseudogap temperature results were suggested that hole filling was the main reason of suppression of superconductivity in this alloys.