Pressure-induced superconductivity in elemental materials

Both experimental and theoretical approaches in our search for superconductivity under pressure are reviewed. We have developed a double extreme condition of very low-temperature down to 50 mK using a He-3/(4) He dilution refrigerator and ultrahigh pressure up to 200 GPa using a diamond-anvil cell (DAC). Experimental techniques producing ultrahigh pressure as well as measuring electrical resistance, magnetization and optical response are developed especially for studying the pressure-induced superconductivity of simple systerns such as elemental materials. The details of these techniques are described in closed integral 1. In closed integral 2, we review several examples of pressure-induced superconductivity observed for the first time by our group. Comparisons between experimental results and theories based on the first principles band calculations are given in closed integral 3. Finally, we point out remaining problems to be solved in further studies in the search for pressure-induced superconductivity,