On the Formation of a Conducting Surface Channel by Ionic‐Liquid Gating of an Insulator

• Published in: Annalen der Physik Vol. 530; no. 10
• Main Authors: Atesci, Hasan, Coneri, Francesco, Leeuwenhoek, Maarten, Bommer, Jouri, Seddon, James R. T., Hilgenkamp, Hans, Van Ruitenbeek, Jan M.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.10.2018
• Subjects: Carrier density; Charge density; Conduction bands; Conductors; Current carriers; electric double layer; Experiments; Glass transition temperature; Ionic liquids; Ions; nanoionics; SrTiO3; Strontium titanates; two‐dimensional conductors
• ISSN: 0003-3804; 1521-3889
• DOI: 10.1002/andp.201700449

Ionic‐liquid gating has become a popular tool for tuning the charge carrier densities of complex oxides. Among these, the band insulator SrTiO3 is one of the most extensively studied materials. While experiments have succeeded in inducing (super)conductivity, the process by which ionic‐liquid gating turns this insulator into a conductor is still under scrutiny. Recent experiments have suggested an electrochemical rather than electrostatic origin of the induced charge carriers. Here, experiments probing the time evolution of conduction of SrTiO3 near the glass transition temperature of the ionic liquid are reported. By cooling down to temperatures near the glass transition of the ionic liquid, the process develops slowly and can be seen to evolve in time. The experiments reveal a process characterized by waiting times that can be as long as several minutes preceding a sudden appearance of conduction. For the conditions applied in our experiments, a consistent interpretation in terms of an electrostatic mechanism for the formation of a conducting path at the surface of SrTiO3 is found. The mechanism by which the conducting surface channel develops relies on a nearly homogeneous lowering of the surface potential until the conduction band edge of SrTiO3 reaches the Fermi level of the electrodes. The time evolution of conduction of SrTiO3 near the glass transition temperature of the ionic liquid is recorded. The experiments reveal waiting times that can be as long as several minutes preceding a sudden appearance of conduction. For the conditions applied, a consistent interpretation is found in terms of a purely electrostatic mechanism for the formationof a conducting path at the surface of SrTiO3.