ON the Nature of Ionic Liquid Gating of La2−xSrxCuO4

Ionic liquids have recently been used as means of modulating the charge carrier properties of cuprates. The mechanism behind it, however, is still a matter of debate. In this paper we report experiments on ionic liquid gated ultrathin La2−xSrxCuO4 films. Our results show that the electrostatic part of gating has limited influence in the conductance of the cuprate in the gate voltage range of 0 to − 2 V. A non-electrostatic mechanism takes over for gate voltages below − 2 V. This mechanism most likely changes the oxygen concentration of the film. The results presented are in line with previous X-ray based studies on ionic liquid gating induced oxygenation of the cuprate materials YBa2Cu3O7−x and La2−xSrxCuO4

On the nature of ionic liquid gating of Nd₂CuO₄ thin films

Recently, ionic liquid gating has been used to modulate the charge carrier properties of metal oxides. The mechanism behind it, however, is still a matter of debate. In this paper, we report experiments on doped and undoped Nd₂CuO₄. We find major resistance drops of the bilayer coupled to observations of the presence of a considerable Faradeic component in the gate current and of the appearance of charge transfer peaks in the cyclic voltammetry data. This leads us to propose a mechanism of gating based on irreversible electrochemical reactions, likely due to trace amounts of contaminations present in the ionic liquid. This work is therefore in line with previous reports confirming the presence of irreversible electrochemistry in ionic liquid gated electron- doped cuprates

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

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