Tailoring the nature and strength of electron-phonon interactions in the SrTiO3(001) 2D electron liquid

Z. Wang, S. McKeown Walker, A. Tamai, Y. Wang, Z. Ristic, F. Y. Bruno, A. de la Torre, S. Riccò, N. C. Plumb, M. Shi, P. Hlawenka, J. Sánchez-Barriga, A. Varykhalov, T. K. Kim, M. Hoesch, P. D. C. King, W. Meevasana, U. Diebold, J. Mesot, B. Moritz, T. P. Devereaux, M. Radovic, F. Baumberger

Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, U.S.A.
Department of Applied Physics, Stanford University, Stanford, CA 94305, U.S.A.
Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY-II, 12489 Berlin, Germany Diamond Light Source, Harwell Campus, Didcot OX11 0DE, UK
SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, UK
School of Physics and NANOTEC-SUT Center of Excellence on Advanced Functional Nanomaterials, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand
Institut für Angewandte Physik, TU Wien, 1040 Wien, Austria
Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, U.S.A.
SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

Nat. Mater. 15 (2016) 835-839

Surfaces and interfaces offer new possibilities for tailoring the many-body interactions that dominate the electrical and thermal properties of transition metal oxides. Here, we use the prototypical two-dimensional electron liquid (2DEL) at the SrTiO3(001) surface to reveal a remarkably complex evolution of electron-phonon coupling with the tunable carrier density of this system. At low density, where superconductivity is found in the analogous 2DEL at the LaAlO3/SrTiO3 interface, our angle-resolved photoemission data show replica bands separated by 100 meV from the main bands. This is a hallmark of a coherent polaronic liquid and implies long-range coupling to a single longitudinal optical phonon branch. In the overdoped regime the preferential coupling to this branch decreases and the 2DEL undergoes a crossover to a more conventional metallic state with weaker short-range electron-phonon interaction. These results place constraints on the theoretical description of superconductivity and allow a unified understanding of the transport properties in SrTiO3-based 2DELs.

Corresponding authors: Zhiming Wang and Felix Baumberger. Reprints also available from Ulrike Diebold (diebold at iap_tuwien_ac_at).

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