The highest critical temperature of superconductivity Tc has been achieved in cuprates: 133 K at ambient pressure and 164 K at high pressures. As the nature of superconductivity in these materials is still not disclosed, the prospects for a higher Tc are not clear. In contrast the Bardeen-Cooper-Schrieffer (BCS) theory gives a clear guide for achieving high Tc: it should be a favorable combination of high frequency phonons, strong coupling between electrons and phonons, and high density of states. These conditions can be fulfilled for metallic hydrogen and covalent hydrogen dominant compounds. Here we found that sulfur hydride transforms at P~90 GPa to metal and superconductor with Tc increasing with pressure to 150 K at ~200 GPa. Moreover we found superconductivity with Tc~190 K in a H2S sample pressurized to P>150 GPa at T>220 K.
Reference: A.P. Drozdov et al., arXiv:1412.0460 [cond-mat.supr-con]
http://arxiv.org/abs/1412.0460
