Metal insulator transition in molecular hydrogens under high pressure

At higher pressures, molecular hydrogen breaks apart, forming extended covalent networks that enable electron delocalization. This metallic hydrogen, a longstanding goal in high-pressure physics for achieving high-temperature superconductivity, remains elusive due to numerous technical challenges. Interestingly, a metal-insulator transition may occur at lower pressures in hydrogen molecular crystals, where H₂ molecules retain their molecular characteristics. We studied this phenomenon using first-principles density functional theory (DFT) calculations with semilocal and hybrid functionals, observing changes in electron distribution that drive the transition. Under increased pressure, H₂ bond lengths stretch, pushing electrons into interstitial sites while maintaining structural stability. This process results in a metal-insulator transition (MIT), where molecular hydrogen shifts from an insulating to a metallic phase. Similar to the extended hydrogen networks in the metallic phase, the interstitial electron states enhance electron-phonon interactions, which are key to achieving high-temperature superconductivity.

We acknowledge the support of the DoD Research and Education Program for Historically Black Colleges and Universities and Minority-Serving Institutions (HBCU/MI) Basic Research Funding under grant No. W911NF2310232., the support of the National Science Foundation (NSF) funds DMR 1848141 and OAC 2117956, and the Camille and Henry Dreyfus Foundation.