Ionic-liquid-gating induced protonation and superconductivity in FeSe, FeSe0.93S0.07, ZrNCl, 1T-TaS2, and Bi2Se3

We report protonation in several compounds by an ionic-liquid-gating method, with optimized gating conditions. This leads to single superconducting phases for several compounds. Non-volatility of protons allow 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. Superconductivity with $T_c$$\approx$15~K for ZrNCl, $\approx$7.2~K for 1$T$-TaS${}_2$, and $\approx$3.8~K for Bi${}_2$Se${}_3$ are induced after protonation. Electric transport in protonated FeSe${}_{0.93}$S${}_{0.07}$ confirms high-temperature superconductivity. Our ${}^1$H NMR measurements on protonated FeSe${}_{1-x}$S${}_x$ reveal enhanced spin-lattice relaxation rate $1{\mathrm{/}}^1{T}_1$ with increasing $x$, which is consistent with LDA calculations that H${}^{+}$ are located in the interstitial sites close to the anions.