Electronic phase diagram of electron-doped cuprate La$_{2-}_{x}$Ce$_{x}$CuO$_{4}$ explored by electrolyte gating

The electrolyte gating technique, which utilizes an electrolyte as a gate dielectric layer of the field-effect transistor, enables us to control a large number of carriers in materials by external voltages. Another advantage of this technique is that it enables stable and quasi-continuous tuning of carrier density in one sample without changing any other parameters, providing a very powerful tool for constructing an electronic phase diagram of a wide variety of materials. We applied this technique to La$_{2-}_{x}$Ce$_{x}$CuO$_{4}$, one of electron-doped cuprate superconductors, and realized gate-induced insulator-to-superconductor transitions. In the presentation, we will mainly discuss evolution of electronic states while changing carrier density, in particular by focusing in the underdoped regime.