Ionic Liquid-Controlled Metal-Insulator Transition And Polarization Switching

In recent years,the electrolyte gating technology,such as ionic liquids gating,has received extensive attention from researchers in the fields of condensed matter physics and materials science.Ionic liquids can be used to control various phase transitions,for example,superconductivity,Mott transition,magnetic phase transition,structural phase transition,etc.,showing great application prospects in many fields,including thermoelectric property control,bionic artificial synapses,smart windows,sensors,flexible semiconductor devices,etc.Ionic liquid gating has now become one of the important ways to explore exotic properties and tune material properties.This article focuses on the effective way of ionic liquid gating,and takes metal-insulator phase transition and ferroelectric domain polarization reversal as the starting point,focusing on the two major material systems of perovskite-type transition metal oxide films and van der Waals layered ferroelectrics.In-depth phase change control research and innovative application research have been carried out.The main research contents are as follows:1.The high-quality Ca_1-xCe_xMnO₃ films were epitaxially grown by pulsed laser deposition technology,and on this basis,an electric double layer field effect transistor was fabricated using ionic liquid as the gate dielectric.In the strong electron corelated Ca_0.95Ce_0.05MnO₃ films,we have realized the reversible phase separation,i.e.the dynamic reversible control between the canted G-type antiferromagnetic metal and the C-type antiferromagnetic insulator.By applying a gate voltage,we experimentally observed reversible metal-insulator phase transition,enhanced colossal magnetoresistance effect(?27 000%for V_g=3.0 V)and large magnetic field memory effect.In addition,we have achieved multi-resistance regulation through the combined use of electric and magnetic fields.The above research results fully indicate that the strong electrostatic field effect at the ionic liquid-oxide film interface can be used as an effective way to control the multiphase coexistence and competition in the strong correlated system,and provides opportunities for the in-depth understanding of the phase separation phenomenon in the manganate system.2.For the first time,van der Waals epitaxy technology was used to successfully prepare a three-dimensional perovskite-type WO₃ film on a natural mica substrate with a layered structure,and a new method for preparing a centimeter-level freestanding WO₃ films was developed.The solid-state ionic gel was used as the gate dielectric to fabricate an all-solid-state transparent flexible transistor,and on this basis,a reversible,volatile,and vacuum-dependent metal-insulator phase transition and electrochromic effect are realized.The in-situ X-ray diffraction technique was used to further characterize the hydrogenation-induced dynamic structural phase transition and the formation of metastable phases.In addition,using the novel resistance change characteristics of WO₃ film,a new prototype vacuum gauge device was designed and constructed.The detection range of the new vacuum gauge can reach 1.0×10^-6 mbar.The above research clarified the physical mechanism of ionic liquid-induced metal-insulator phase transition of WO₃ films,and explored the potential new applications of ionic liquid gating.3.Without applying an external electric field,we have successfully realized large-area ferroelectric polarizaition switching using ionic liquid for the first time in the van der Waals layered ferroelectric material Cu In P₂S₆.At room temperature,the cations in the ionic liquid are spontaneously adsorbed on the ferroelectric surface,and an additional electrostatic field is provided to realize the inversion of dipoles.Furthermore,the selective adsorption of anions is used to realize the reversible polarization reversal.This method overcomes the shortcomings that electrical switching will destroy the ferroelectricity of Cu In P₂S₆,and provides a new method for realizing erasable ferroelectric printing without power consumption.It also provides a paradigm for artificially modulating the ferroelectric-liquid interface structures and novel interface effects.