New metals and superconductors from ionic liquid gating

One of the central goals of condensed matter physics is to tune the properties of solids by applying external stimuli. One very promising method is to change the density of charge carriers.  Ionic liquid gating, as an emerging and enabling technique, is able to raise the carrier doping limit by orders of magnitude over that of traditional solid gating. Owing to such high doping capabilities (up to 1015 electrons or holes/cm2), ionic liquid gated field-effect transistors have been extensively exploited as powerful platforms to induce various exotic physical phenomena, including insulator-metal transition, gate-induced superconductivity [1], and the occurrence of cross quantum capacitance [2]. On the other hand, given the concurrent existence of complex electron-electron interaction effects, the underlying physical mechanisms of such intriguing phenomena remain elusive.

Schematic of an ionic liquid gated field-effect transistor, showing the gate electrode as well as the electrical circuit used to bias and measure the device.

In this project, you will exploit ionic liquid gated field-effect transistors to search for interface-based new metals and superconductors from otherwise intrinsic semiconductors and semi-metals. Specific systems may include two-dimensional (2D) or quasi-2D delafossite oxides and copper-based high temperature superconductors. The aim of this project is to understand how the electron-electron interactions play a vital role in these correlated electron systems. A more ambitious aim is to gain new insights into the superconducting mechanisms of the high temperature superconductors and beyond, including potentially discoveries of new superconducting platforms for topological quantum computing.

This project would suit a student with a background in solid state physics or material science, who is interested in nanofabrication and performing transport measurements at low temperature. The majority of the experimental work will be performed at MPI CPfS Dresden, in close collaboration with St Andrews.

[1] D. Costanzo, H. Zhang, B.A. Reddy, H. Berger and A.F. Morpurgo
Tunnelling spectroscopy of gate-induced superconductivity in MoS2
Nature Nanotechnology 13, 483-488 (2018)
[2] H. Zhang, C. Berthod, H. Berger, T. Giamarchi and A.F. Morpurgo
Band filling and cross quantum capacitance in ion-gated semiconducting transition metal dichalcogenide monolayers
Nano Letters 19,  8836–8845 (2019)

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