title: Polaronic metal state at the LaAlO3/SrTiO3 interface.
abstract: Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 that hosts a two-dimensional electron system. Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LaAlO3 overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland.|EMPA, Swiss Federal Laboratories for Materials Science &Technology, Ueberlandstrasse 129, Duebendorf 8600, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Cancellieri
authors.affiliation: RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: A S
authors.initials: AS
authors.lastname: Mishchenko
authors.affiliation: Materials Theory, ETH Zurich, Wolfgang-Pauli-Strasse 27, Zürich CH-8093, Switzerland.|Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3 3012 Bern, Switzerland.
authors.forename: U
authors.initials: U
authors.lastname: Aschauer
authors.affiliation: CNR-IOM, Istituto Officina dei Materiali, Cittadella Universitaria, Cagliari, Monserrato 09042-I, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Filippetti
authors.affiliation: Materials Theory, ETH Zurich, Wolfgang-Pauli-Strasse 27, Zürich CH-8093, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Faber
authors.affiliation: Institute of Physics, Bijenička 46, 10000 Zagreb, Croatia.
authors.forename: O S
authors.initials: OS
authors.lastname: Barišić
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland.
authors.forename: V A
authors.initials: VA
authors.lastname: Rogalev
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Schmitt
authors.affiliation: RIKEN Center for Emergent Matter Science, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.|Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Nagaosa
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland.
authors.forename: V N
authors.initials: VN
authors.lastname: Strocov
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