Nature 525, 73–76 (2015)

Below their superconducting critical temperature, Tc, superconductors show zero resistance. The highest Tc reported so far has been found in unconventional superconductors. These materials do not follow the Bardeen–Cooper–Schrieffer (BCS) theory (the first microscopic model to explain the superconductivity), and the mechanisms leading to their superconductivity are not well understood, which makes it difficult to predict their properties. Now, Alexander Drozdov and colleagues show that H2S, under pressures of around 200 GPa, becomes a conventional superconductor with a record high Tc of 203 K. Based on spectroscopic measurements and theoretical calculations, the authors claim that H2S decomposes forming H3S at high pressure. This material is, in fact, the first superconductor to be predicted that was subsequently confirmed experimentally. This study also demonstrates that the BCS theory can be used to look for room-temperature superconductivity in other hydrogen-based materials.