Superconductivity from insulating elements under high pressure

• Even insulating molecule can become metal and superconductor by pressure with relatively high Tc.
• The highest Tc is observed in sulfur with 17 K at 160 GPa.
• Hydrogen is the best candidate of the highest Tc element.

The insulating and superconducting states would seem to have very different characteristics. Can any insulator become a superconductor? One proven method, doping an insulating material with carriers, can create itinerant states inside the gap between the conduction and valence bands. Another method is to squeeze the structure by applying pressure. Pressure can expand the bandwidth and also narrow the energy band gap. So the first step to turn an insulator into a superconductor is to make it metallic. Here we review our experimental research and results on superconductivity induced by applying pressure to insulating molecular systems such as elemental molecules.