Abstract
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 V. A non-electrostatic mechanism takes over for gate voltages below 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.
Highlights
Changing the charge carrier density by means of gating is the crux of today’s technology, where fields of up to 10 MV/cm are used in transistors to change semiconductor properties
Dubuis et al [11] argued that the electric field of the electric double layer drives a redistribution of the oxygen atoms in the basal planes of the cuprate in an electrostatic fashion, while others have suggested an electrochemical process leading to oxygenation of the cuprate [12,13]
We observe that ionic liquids (ILs) gating induces superconductivity in La1.95Sr0.05CuO4, even when the film has a thickness of 30 unit cells (UC) (Figure 1A)
Summary
Changing the charge carrier density by means of gating is the crux of today’s technology, where fields of up to 10 MV/cm are used in transistors to change semiconductor properties. With a ∼1 nm separation within the double layer charge carrier densities of up to 8 × 1014 cm−2 are achievable [1], making it possible to induce insulator-to-superconductor [2,3,4] and metal-to-insulator transitions [5,6,7]. This technique is driven by an electrostatic mechanism, and holds for many materials [8,9].
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