Lowerature Charging Dynamics of the Ionic Liquid and Its Gating Effect on FeSe_0.5Te_0.5 Superconducting Films

Ionic liquids (ILs) have been investigated extensively because of their unique ability to form the electric double layer (EDL), which induces high electrical field. For certain materials, lowerature IL charging is needed to limit the electrochemical etching. Here, we report our investigation of the lowerature charging dynamics in two widely used ILs-DEME-TF₂N and C₄mim-TF₂N. Results show that the formation of the EDL at â220 K requires several hours relative to milliseconds at room temperature, and an equivalent voltage V_e is introduced as a measure of the EDL formation during the biasing process. The experimental observation is supported by molecular dynamics simulation, which shows that the dynamics are logically a function of gate voltage, time, and temperature. To demonstrate the importance of understanding the charging dynamics, a 140 nm thick FeSe_0.5Te_0.5 film was biased using the DEME IL, showing a tunable T_c between 18 and 35 K. Notably, this is the first observation of the tunability of the T_c in thick film FeSe_0.5Te_0.5 superconductors.