Synthesis of superhydrides and metallization of hydrogen at high pressures*

Hydrogen and hydrogen-rich materials are expected to possess spectacular properties such as high-temperature superconductivity at extreme pressure-temperature conditions where the crossovers to monatomic phases and formations of superhydrides would occur. Recent theoretical studies predicted the formations of such superhydrides at the experimentally accessible pressure range and some of them have been recently synthesized such as, for example, H₃S. The transformation of molecular hydrogen to monatomic metallic hydrogen at high pressures in solid and fluid states remains controversial as the reported behaviors (both in theory and experiment) differ in the character and in the pressure-temperature range. I will review the latest results in the field obtained using different experimental and theoretical approaches and will present new results the plasma phase transition in hydrogen and synthesis of novel superhydrides including uranium hydrides. I will also discuss the complexities of theoretical and experimental (static and dynamic) studies of hydrogen-rich materials at extreme conditions which remain a challenge and continue inspiring researchers for further technical developments.