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As a prototypical Mott insulator with ferromagnetic ordering, YTiO3 (YTO) is of great interest in the study of strong electron correlation effects and orbital ordering. Here we report the first molecular beam epitaxy (MBE) growth of YTO films, combined with theoretical and experimental characterizations of the electronic structure and charge transport properties. The obstacles of YTO MBE growth are discussed and potential routes to overcome them are proposed. DC transport and Seebeck measurements on thin films and bulk single crystals identify p-type Arrhenius transport behavior with an activation energy of Gê+0.17eV in thin films, consistent with the energy barrier for small hole polaron migration from hybrid density functional theory calculations. Hard x-ray photoelectron spectroscopy measurements show the lower Hubbard band at 1.1 eV below the Fermi level, whereas a Mott-Hubbard band gap of Gê+1.5eV is determined from photoluminescence measurements. These findings provide critical insight into the electronic band structure of YTO and related materials.
Bibliographical noteFunding Information:
This work was primarily supported by the U.S. Department of Energy through the University of Minnesota Center for Quantum Materials under Award No. DE-SC0016371. Parts of this work were carried out at the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nano Coordinated Infrastructure (NNCI) under Award No. ECCS-1542202. Structural characterizations were carried out at the University of Minnesota Characterization Facility, which receives partial support from NSF through the MRSEC Program. I.L. and A.J. acknowledge support from the NSF Early Career Award Grant No. DMR-1652994. H.C. and M.F.D. acknowledge support from NSF Grant No. DMR-1839056. It made use of the computing resources provided by the Extreme Science and Engineering Discovery Environment (XSEDE), supported by the National Science Foundation Grant No. ACI-1053575. The HAXPES measurements were performed while N.F.Q. held a National Institute of Standards and Technology (NIST) National Research Council (NRC) Research Postdoctoral Associateship Award at the Material Measurement Laboratory. We thank Diamond Light Source for access to beamline I-09 (SI17449-1) that contributed to the results presented here.
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