Ionic-Liquid-Gating Induced Protonation and Superconductivity in FeSe, FeSe_0.93S_0.07, ZrNCl, 1T-TaS_2 and Bi_2Se_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_\rm c is enhanced to 43.5 K for FeSe_0.93S_0.07, and 41 K for FeSe after protonation. Superconducting transitions with T_\rm c \sim 15 K for ZrNCl, \sim7.2 K for 1T-TaS_2, and \sim3.8 K for Bi_2Se_3 are induced after protonation. Electric transport in protonated FeSe_0.93S_0.07 confirms high-temperature superconductivity. Our ^1H nuclear magnetic resonance (NMR) measurements on protonated FeSe_1-xS_x reveal enhanced spin-lattice relaxation rate 1/^1T_1 with increasing x, which is consistent with the LDA calculations that H^+ is located in the interstitial sites close to the anions.