title: Giant reversible, facet-dependent, structural changes in a correlated-electron insulator induced by ionic liquid gating.
abstract: The use of electric fields to alter the conductivity of correlated electron oxides is a powerful tool to probe their fundamental nature as well as for the possibility of developing novel electronic devices. Vanadium dioxide (VO2) is an archetypical correlated electron system that displays a temperature-controlled insulating to metal phase transition near room temperature. Recently, ionic liquid gating, which allows for very high electric fields, has been shown to induce a metallic state to low temperatures in the insulating phase of epitaxially grown thin films of VO2. Surprisingly, the entire film becomes electrically conducting. Here, we show, from in situ synchrotron X-ray diffraction and absorption experiments, that the whole film undergoes giant, structural changes on gating in which the lattice expands by up to ∼3% near room temperature, in contrast to the 10 times smaller (∼0.3%) contraction when the system is thermally metallized. Remarkably, these structural changes are fully reversible on reverse gating. Moreover, we find these structural changes and the concomitant metallization are highly dependent on the VO2 crystal facet, which we relate to the ease of electric-field-induced motion of oxygen ions along chains of edge-sharing VO6 octahedra that exist along the (rutile) c axis.
authors.affiliation: International Business Machines Almaden Research Center, San Jose, CA 95120;
authors.forename: Jaewoo
authors.initials: J
authors.lastname: Jeong
authors.affiliation: International Business Machines Almaden Research Center, San Jose, CA 95120;
authors.forename: Nagaphani B
authors.initials: NB
authors.lastname: Aetukuri
authors.affiliation: International Business Machines Almaden Research Center, San Jose, CA 95120; Graduate School of Excellence Materials Science in Mainz, University of Kaiserslautern, 67663 Kaiserslautern, Germany;
authors.forename: Donata
authors.initials: D
authors.lastname: Passarello
authors.affiliation: Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545; and.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Conradson
authors.affiliation: International Business Machines Almaden Research Center, San Jose, CA 95120;
authors.forename: Mahesh G
authors.initials: MG
authors.lastname: Samant
authors.affiliation: International Business Machines Almaden Research Center, San Jose, CA 95120; Max Planck Institute for Microstructure Physics, 06120 Halle, Germany Stuart.Parkin@icloud.com.
authors.forename: Stuart S P
authors.initials: SS
authors.lastname: Parkin
keywords: EXAFS; correlated oxides; electrolyte gating; metal–insulator transition; vanadium dioxide