Observation of a first order phase transition to metal hydrogen near 425 GPa

Abstract

Hydrogen has been the essential element in the development of atomic and molecular physics1). Moving to the properties of dense hydrogen has appeared a good deal more complex than originally thought by Wigner and Hungtinton in their seminal paper predicting metal hydrogen2): the electrons and the protons are strongly coupled to each other and ultimately must be treated equally3)4). The determination of how and when molecular solid hydrogen will transform into a metal is the stepping stone towards a full understanding of the quantum-many body properties of dense hydrogen. The quest for metal hydrogen has pushed major developments of modern experimental high pressure physics, yet the various claims of its observation over the past 30 years have remained controversial5)6)7). Here we show a first order phase transition near 425 GPa from insulator molecular solid hydrogen to metal hydrogen. Pressure in excess of 400 GPa could be achieved by using the recently developed Toroidal Diamond Anvil Cell (T-DAC)8). The structural and electronic properties of dense solid hydrogen at 80 K have been characterized by synchrotron infrared spectroscopy. The continuous vibron frequency shift and the electronic band gap closure down to 0.5 eV, both linearly evolving with pressure, point to the stability of the insulator C2/c-24 phase up to the metallic transition. Upon pressure release, the metallic state transforms back to the C2/c-24 phase with almost no hysteresis, hence suggesting that the metallization proceeds through a structural transformation within the molecular solid, presumably to the Cmca-12 structure. Our results are in good agreement with the scenario recently disclosed by an advanced calculation able to capture many-body electronic correlations9).

References in corpus (8)

• Conventional superconductivity at 203 K at high pressures
• Evidence for superconductivity above 260 K in lanthanum superhydride at megabar pressures
• Observation of the Wigner-Huntington Transition to Solid Metallic Hydrogen
• Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures
• Anharmonic effects in atomic hydrogen: superconductivity and lattice dynamical stability
• Towards a Predictive First-Principles Description of Solid Molecular Hydrogen with Density-Functional Theory
• Strong Isotopic Effect in Phase II of Dense Solid Hydrogen and Deuterium
• Prediction of a Mobile Solid State in Dense Hydrogen under High Pressures

Cited by in corpus (4)

• Energy gap closure of crystalline molecular hydrogen with pressure
• Beyond the Fröhlich Hamiltonian: Path integral treatment of large polarons in anharmonic solids
• Improving Resolution of Solid State NMR in Dense Molecular Hydrogen
• Comment on: Observation of a first order phase transition to metal hydrogen near 425 GPa