Ionic-Liquid-Gating Induced Protonation and Superconductivity in FeSe, FeSe$_{0.93}$S$_{0.07}$, ZrNCl, 1$T$-TaS$_2$ and Bi$_2$Se$_3$

We report protonation in several compounds by an ionic-liquid-gating method, under optimized gating conditions. This leads to single superconducting phases for several compounds. Non-volatility of protons allows post-gating magnetization and transport measurements. The superconducting transition temperature T c is enhanced to 43.5 K for FeSe 0.93 S 0.07 , and 41 K for FeSe after protonation. Superconducting transitions with T c ~ 15 K for ZrNCl, ~7.2 K for 1T-TaS 2 , and ~3.8 K for Bi 2 Se 3 are induced after protonation. Electric transport in protonated FeSe 0.93 S 0.07 confirms high-temperature superconductivity. Our 1 H nuclear magnetic resonance (NMR) measurements on protonated FeSe 1−x S x reveal enhanced spin-lattice relaxation rate 1/1 T 1 with increasing x, which is consistent with the LDA calculations that H + is located in the interstitial sites close to the anions.