Influence of fluctuation conductivity on the high-field magnetoresistivity in epitaxial La2−xSrxCuO4 thin films

A large positive magnetoresistivity (up to tens of percents) is observed for underdoped superconducting La2-xSrxCuO4 epitaxial thin films at temperatures far above the superconducting critical temperature Tc. For the underdoped samples, this magnetoresistance far above Tc cannot be described solely by the Kohler effect and we believe it is to be attributed to the influence of superconducting fluctuations or the existence of preformed pairs. In the underdoped regime, the large magnetoresistance is only observed when low-temperatures superconductivity occurs. The strong magnetoresistivity, which persists even at temperatures far above Tc, can be related to the pairs forming the superconducting phase below Tc. Our observations support the idea of a close relation between the pseudogap and the superconducting gap and provide new indications for the presence of pairs above Tc.