  We present detailed studies of the superconductivity in high-pressure H3S.
X-ray diffraction measurements show that cubic Im-3m H3S was synthesized from
elemental sulfur and hydrogen donor ammonia borane (NH3BH3). Our electrical
transport measurements confirm superconductivity with a transition temperature
Tc = 197 K at 153 GPa. From the analysis of both the normal state resistivity
and the slope of the critical field, we conclude that the superconductivity is
described by clean-limit behaviour. A significant broadening of the resistive
transition in finite magnetic field is found, as expected for superconductors.
We identify a linear temperature-over-field scaling of the resistance at the
superconducting transition which is not described by existing theories.
