Superconductor-Insulator Transition of Cuprate Thin Films Driven by Tuning of In-Plane Epitaxial Strain with a Buffer Layer

In order to finely tune the epitaxial strain we propose to insert a buffer layer of LaSrAl1-zGazO4 between a superconducting cuprate thin-film and LaSrAlO4 substrate. Thin films of La1.875Ba0.125CuO4/LaSrAl1-zGazO4 (LBCO/LSAGO) grown by pulsed laser deposition have been characterized by x-ray diffraction and transport measurements. The c-axis length of LBCO on the buffer layer shows a systematic change with z indicating that the epitaxial strain is reasonably controlled. Superconducting transition temperature of LBCO/LSAGO films smoothly decreases with increasing z, and finally diminishes. Besides, LBCO films show systematic increase of normal-state resistivities with increasing z. However, comparing with single crystals of La2-xSrxCuO4, Hall coefficients of insulating film is much lower than expected. Therefore, the phenomena cannot be explained by nominal change of carrier and indicates that the epitaxial strain causes certain modification on the shape of Fermi surface.