  Recently, an extremely high superconducting temperature (Tc) of ~200 K has
been reported in the sulfur hydride system above 100 GPa. This result is
supported by theoretical predictions and verified experimentally. The crystal
structure of the superconducting phase was also identified experimentally,
confirming the theoretically predicted structure as well as a decomposition
mechanism from H2S to H3S+S. Even though nuclear resonant scattering has been
successfully used to provide magnetic evidence for a superconducting state, a
direct measurement of the important Meissner effect is still lacking. Here we
report in situ alternating-current magnetic susceptibility measurements on
compressed H2S under high pressures. It is shown that superconductivity
suddenly appears at 117 GPa and that Tc reaches 183 K at 149 GPa before
decreasing monotonically with a further increase in pressure. This evolution
agrees with both theoretical calculations and earlier experimental
measurements. The idea of conventional high temperature superconductivity in
hydrogen-dominant compounds has thus been realized in the sulfur hydride system
under hydrostatic pressure, opening further exciting perspectives for possibly
realizing room temperature superconductivity in hydrogen-based compounds.
