Distinct electronic structure of the electrolyte gate-induced conducting phase in vanadium dioxide revealed by high-energy photoelectron spectroscopy

Julie Karel, Carlos E. ViolBarbosa, Janos Kiss, Jaewoo Jeong, Nagaphani Aetukuri, Mahesh G. Samant, Xeniya Kozina, Eiji Ikenaga, Gerhard H. Fecher, Claudia Felser, Stuart S P Parkin, Stuart S.P. Parkin

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24 Citations (Scopus)

Abstract

The development of new phases of matter at oxide interfaces and surfaces by extrinsic electric fields is of considerable significance both scientifically and technologically. Vanadium dioxide (VO2), a strongly correlated material, exhibits a temperature-driven metal-to-insulator transition, which is accompanied by a structural transformation from rutile (high-temperature metallic phase) to monoclinic (low-temperature insulator phase). Recently, it was discovered that a low-temperature conducting state emerges in VO2 thin films upon gating with a liquid electrolyte. Using photoemission spectroscopy measurements of the core and valence band states of electrolyte-gated VO2 thin films, we show that electronic features in the gate-induced conducting phase are distinct from those of the temperature-induced rutile metallic phase. Moreover, polarization-dependent measurements reveal that the V 3d orbital ordering, which is characteristic of the monoclinic insulating phase, is partially preserved in the gate-induced metallic phase, whereas the thermally induced metallic phase displays no such orbital ordering. Angle-dependent measurements show that the electronic structure of the gate-induced metallic phase persists to a depth of at least ∼40 Å, the escape depth of the high-energy photoexcited electrons used here. The distinct electronic structures of the gate-induced and thermally induced metallic phases in VO2 thin films reflect the distinct mechanisms by which these states originate. The electronic characteristics of the gate-induced metallic state are consistent with the formation of oxygen vacancies from electrolyte gating. 

Original languageEnglish
Pages (from-to)5784-5789
Number of pages6
JournalACS Nano
Volume8
Issue number6
DOIs
Publication statusPublished - 24 Jun 2014
Externally publishedYes

Keywords

  • VO2
  • Ionic liquid electrolyte gating
  • Orbital polarization
  • X-ray photoelectron spectroscopy

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