We systematically study the structural and electronic properties of very thin cuprate films. Our direct angle resolved photoemission spectroscopy (ARPES) measurements on the low binding energy electronic structure of La2-xSrxCuO4 (LSCO) films confirmed that the Fermi surface evolves with doping, but changes even more significantly with growth-induced compressive strain. For a given doping, the in-plane compressive strain enhances TC's and modifies the 2-dimensional hole-like Fermi surface as to appear more electron-like. In contrast, the in-plane tensile strain reduces TC (suppressing superconductivity for huge tensile strain) and shows 3-dimensional ARPES dispersion with a corresponding 3-dimensional Fermi surface. To account for these striking changes in electronic structure and superconductivity, the out-of-plane states should be taken into account, as well as some subtle changes in the associated atomic distances.
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