Volatile two-dimensional electron gas in ultrathin ${\mathrm{BaTiO}}_{3}$ films

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Volatile two-dimensional electron gas in ultrathin ${BaTiO}_{3}$ films

Peter Lutz, Simon Moser, Vedran Jovic, Young Jun Chang, Roland J. Koch, Søren Ulstrup, Ji Seop Oh, Luca Moreschini, Sara Fatale, Marco Grioni, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Hendrik Bentmann, and Friedrich Reinert

Phys. Rev. Materials 2, 094411 – Published 28 September 2018

Abstract

We investigate the metallic surface state in ultrathin films of ${BaTiO}_{3}$ by angle-resolved photoemission spectroscopy. We find Fermi-surface contours derived from the Ti $3 d t_{2 g}$ conduction band, similar as in ${SrTiO}_{3}$ but with broader spectral features due to enhanced quasiparticle scattering. Oxygen vacancies created in the x-ray beam spot allow for reversible in situ doping control up to surface carrier densities as high as $10^{14} {cm}^{- 2}$ , but vacancy migration into the subsurface at $T \geq 285 K$ quenches the surface state. Our analysis suggests that the charge state of oxygen vacancies in ultrathin films is predominantly $2 +$ , which limits charge-carrier trapping and the formation of localized defect states.

Received 10 May 2017
Revised 9 July 2017

DOI:https://doi.org/10.1103/PhysRevMaterials.2.094411

Physics Subject Headings (PhySH)

Electrical conductivity Electrical properties Ferroelectricity

Two-dimensional electron gas Ultrathin films

Angle-resolved photoemission spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Peter Lutz¹, Simon Moser^2,*, Vedran Jovic², Young Jun Chang^2,3, Roland J. Koch², Søren Ulstrup², Ji Seop Oh^2,4,5, Luca Moreschini², Sara Fatale⁶, Marco Grioni⁶, Chris Jozwiak², Aaron Bostwick², Eli Rotenberg², Hendrik Bentmann¹, and Friedrich Reinert¹

¹Experimentelle Physik VII, Röntgen Research Center for Complex Materials (RCCM), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
²Advanced Light Source (ALS), Berkeley, California 94720, USA
³Department of Physics, University of Seoul, Seoul 02504, Republic of Korea
⁴Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea
⁵Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea
⁶Institute of Physics (IPHYS), Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland