Dominant role of processing temperature in electric field induced superconductivity in layered ZrNBr

Recently, as a novel technique, electronic double-layer transistors (EDLTs) with ionic liquids have shown strong potential for tuning the electronic states of correlated systems. EDLT induced local carrier doping can always lead to dramatic changes in physical properties when compared to parent materials, e.g., insulating-superconducting transition. Generally, the modification of gate voltage ($V_{\rm G}$) in EDLT devices produces a direct change on the doping level, whereas the processing temperature ($T_{\rm G}$) at which $V_{\rm G}$ is applied only assists the tuning process. Here, we report that the processing temperature $T_{\rm G}$ plays a dominant role in the electric field induced superconductivity in layered ZrNBr. When applying $V_{\rm G}$ at $T_{\rm G}\geq$ 250 K, the induced superconducting (SC) state permanently remains in the material, which is confirmed in the zero resistance and diamagnetism after long-time relaxation at room temperature and/or by applying reverse voltage, whereas the solid/liquid interface induced reversible insulating-SC transition occurs at $T_{\rm G}\leq$ 235 K. These experimental facts support another electrochemical mechanism that electric field induced partial deintercalation of Br ions could cause permanent electron doping to the system. Our findings in this study will extend the potential of electric fields for tuning bulk electronic states in low-dimension systems.