Room temperature metal-insulator transition in as grown (La1-xSrx)(y)MnO3 thin films deposited by molecular beam epitaxy

We have fabricated by an in situ process (La1-xSrx)(y)MnO3 epitaxial thin films by Molecular Beam Epitaxy using a low partial pressure (congruent to2 x 10(-5) torr) Of O-2+5% ozone. Reflected High Energy Electron Diffraction analysis has been performed during the growth process to check the structural properties of the films. The samples have not been subjected to any in situ or ex situ post deposition annealing procedure. Thin films on different substrates (SrTiO3, LaAlO3, NdGaO3) and with different thickness have been fabricated to compare the transport properties and investigate the effects of the epitaxial strain. For compositions around x = 0.3. Alletal-Insulator (MI) transitions at temperature as high as T-MI = 340 K have been observed in thin films few nanometers thick. Resistivity versus temperature curves measured or) samples deposited in the same run onto different substrates, have shown clear effects related to the epitaxial strain. These results are very promising for a deeper understanding of the physical mechanisms at work in manganites and in view of the future fabrication of manganite-based heterostructures for electronic applications.