Ionic gating in metallic superconductors: A brief review

Abstract

Ionic gating is a very popular tool to investigate and control the electric charge transport and electronic ground state in a wide variety of different materials. This is due to its capability to induce large modulations of the surface charge density by means of the electric-double-layer field-effect transistor (EDL-FET) architecture, and has been proven to be capable of tuning even the properties of metallic systems. In this short review, I summarize the main results which have been achieved so far in controlling the superconducting (SC) properties of thin films of conventional metallic superconductors by means of the ionic gating technique. I discuss how the gate-induced charge doping, despite being confined to a thin surface layer by electrostatic screening, results in a long-range "bulk" modulation of the SC properties by the coherent nature of the SC condensate, as evidenced by the observation of suppressions in the critical temperature of films much thicker than the electrostatic screening length, and by the pronounced thickness-dependence of their magnitude. I review how this behavior can be modelled in terms of proximity effect between the charge-doped surface layer and the unperturbed bulk with different degrees of approximation, and how first-principles calculations have been employed to determine the origin of an anomalous increase in the electrostatic screening length at ultrahigh electric fields, thus fully confirming the validity of the proximity effect model. Finally, I discuss a general framework - based on the combination of ab-initio Density Functional Theory and the Migdal-Eliashberg theory of superconductivity - by which the properties of any gated thin film of a conventional metallic superconductor can be determined purely from first principles.

arXiv comment11 pages, 4 figures

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• Optimizing one dimensional superconducting diodes: Interplay of Rashba spin-orbit coupling and magnetic fields
• Anomalous metallic phase in molybdenum disulphide induced via gate-driven organic ion intercalation
• Reversible Tuning of Superconductivity in Ion-Gated NbN Ultrathin Films by Self-Encapsulation with a High-$\kappa$ Dielectric Layer
• Facile synthesis of palladium hydride via ionic gate-driven protonation using a deep eutectic solvent
• Interfacial control of vortex-limited critical current in type II superconductor films
• Optical grade bromide-based thin film electrolytes
• Band structure of organic-ion-intercalated (EMIM)${}_x$FeSe superconductor
• Effect of Underlayer Induced Charge Carrier Substitution on the Superconductivity of Ti40V60 Alloy Thin Films