Evidence for the Pair Formation Far above Tc in Epitaxial La2-xSrxCuO4 Thin Films

A large positive magnetoresistivity (up to ten percent or more) is observed for both under-doped and over-doped superconducting La_2-xSr_xCuO₄ epitaxial thin films at temperatures far above the superconducting critical temperature T_c. This magnetoresistivity can be related to the pairs eventually forming the superconducting phase at low temperatures. Our observations support the idea of a close relation between the pseudogap and the superconducting gap and provide new indications for the presence of pre-pairs above T_c.