title: Mechanisms of charge transfer and redistribution in LaAlO3/SrTiO3 revealed by high-energy optical conductivity.
abstract: In condensed matter physics the quasi two-dimensional electron gas at the interface of two different insulators, polar LaAlO3 on nonpolar SrTiO3 (LaAlO3/SrTiO3) is a spectacular and surprising observation. This phenomenon is LaAlO3 film thickness dependent and may be explained by the polarization catastrophe model, in which a charge transfer of 0.5e(-) from the LaAlO3 film into the LaAlO3/SrTiO3 interface is expected. Here we show that in conducting samples (≥ 4 unit cells of LaAlO3) there is indeed a ~0.5e(-) transfer from LaAlO3 into the LaAlO3/SrTiO3 interface by studying the optical conductivity in a broad energy range (0.5-35 eV). Surprisingly, in insulating samples (≤ 3 unit cells of LaAlO3) a redistribution of charges within the polar LaAlO3 sublayers (from AlO2 to LaO) as large as ~0.5e(-) is observed, with no charge transfer into the interface. Hence, our results reveal the different mechanisms for the polarization catastrophe compensation in insulating and conducting LaAlO3/SrTiO3 interfaces.
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore [3] Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore.
authors.forename: T C
authors.initials: TC
authors.lastname: Asmara
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore.
authors.forename: A
authors.initials: A
authors.lastname: Annadi
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore [3] Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore.
authors.forename: I
authors.initials: I
authors.lastname: Santoso
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore [3] Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore.
authors.forename: P K
authors.initials: PK
authors.lastname: Gogoi
authors.affiliation: Hamburger Synchrotronstrahlungslabor (HASYLAB) at Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, 22603 Hamburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Kotlov
authors.affiliation: Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore.
authors.forename: H M
authors.initials: HM
authors.lastname: Omer
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore [3] Department of Physics, Center for Ion Beam Applications (CIBA), National University of Singapore, Singapore 117542, Singapore.
authors.forename: M
authors.initials: M
authors.lastname: Motapothula
authors.affiliation: 1] Department of Physics, National University of Singapore, Singapore 117576, Singapore [2] Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore [3] Department of Physics, Center for Ion Beam Applications (CIBA), National University of Singapore, Singapore 117542, Singapore.
authors.forename: M B H
authors.initials: MB
authors.lastname: Breese
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Institut für Angewandte Physik, Universität Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany [3] Center for Free Electron Laser Science (CFEL), Notkesstrasse 85, D-22607 Hamburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Rübhausen
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore [3] Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore.
authors.forename: T
authors.initials: T
authors.lastname: Venkatesan
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore.
authors.lastname: Ariando
authors.affiliation: 1] NUSNNI-NanoCore, National University of Singapore, Singapore 117411, Singapore [2] Department of Physics, National University of Singapore, Singapore 117576, Singapore [3] Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore.
authors.forename: A
authors.initials: A
authors.lastname: Rusydi