Liquid Metallic Hydrogen produced in the lab at static Megabar pressures
Producing metallic hydrogen (MH) in the laboratory has been a challenge for over 80 years. Wigner and Huntington predicted that when hydrogen was compressed to high density at low temperature, the molecules would dissociate to an atomic lattice that is metallic; the required pressure is now estimated to be over 4 million atmospheres.
MH was later predicted to be a high temperature superconductor with possible metastability. Subsequent theory predicted an alternate path to MH: hydrogen would dissociate at an intermediate pressure when heated to high temperatures. Thus, when hydrogen is compressed to ~1-2 megabars and heated, the solid melts into liquid molecular hydrogen and with further heating the molecules dissociate to form liquid atomic metallic hydrogen. This first-order phase transition to liquid MH has been observed in the laboratory for static pressures of 1-2 megabar and temperatures of 1000-2000 K. Metallic behavior is detected by observing transmittance and reflectance which abruptly change to that of a metal.
Most of the hydrogen in our Solar System is dense liquid metallic hydrogen. Knowledge of the transport properties and thermodynamic state hydrogen when this insulator-metal phase transition to MH takes place is crucial for the understanding of astrophysical giants such as Saturn or Jupiter. Yet despite some pioneering shock-wave experiments in 1996 using gas-gun and later in 1998, 2002 using laser and magnetic compression, static experiments, used in current work, would enable bench-top studies of the most abundant metal in the Universe as well as a direct probe to the interiors of giant planets.
The results present a significant advance over previous shock-wave work because temperature measurements have been out of experimental reach for shock experiments above 1 Mbar. The current data, with measured P and T, presents the first conclusive experimental evidence of the location of the insulator-metal transition in dense hydrogen.
More information:
Evidence for a first order phase transition to metallic hydrogen, Physical Review B 26 April 2016: Vol. 93 no. 15 pp. 155128
dx.doi.org/10.1103/PhysRevB.93.155128
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