Pseudogap opening, superconducting fluctuation and vortex-like excitation above Tc in slightly overdoped Bi2Sr2CaCu2O8+δ

The magnetoresistance, Hall effect and Nernst effect of slightly overdoped Bi2Sr2CaCu2O8+δ single crystals were measured for both normal state and mixed state. The superconducting transition temperature (Tc0) and the pseudogap opening temperature (T*) determined from the temperature dependence of resistivity are 86.5K and 120K respectively, while the onset temperature (TO) of vortex-like excitation detected by Nernst effect is about 105K, which is consistent with the onset temperature of superconducting fluctuation determined from magnetoresistance and Hall coefficient measurement. This result indicates that both pseudogap opening and superconducting fluctuation exist above Tc in the slightly overdoped region of electronic phase diagram of cuprates. In contrast to the underdoped case, the narrower temperature range of superconducting fluctuation in the slightly overdoped region could be understood by the Ginzburg–Landau fluctuation theory.