Saturday, January 28, 2017

Metallic Hydrogen Research

Metallic hydrogen is a kind of degenerate matter, a phase of hydrogen in which it behaves like an electrical conductor. This phase was predicted theoretically by Eugene Wigner and Hillard Bell Huntington in 1935.

At high pressure and temperatures, metallic hydrogen might exist as a liquid rather than a solid, and researchers think it is present in large amounts in the gravitationally compressed interiors of Jupiter, Saturn, and in some extrasolar planets.

                                                      Gas giants such as Jupiter (pictured
                                                     above) and Saturn may contain large
                                                     amounts of metallic hydrogen
                                                    (depicted in grey) and metallic helium

In October 2016, there were claims that metallic hydrogen has been observed in the laboratory at a pressure of around 495 gigapascals (4,950,000 bar; 4,890,000 atm; 71,800,000 psi). As of January 2017, these findings have not yet been replicated. Some observations consistent with metallic behavior had previously been reported, such as the reported observation of some new phases of solid hydrogen under static conditions, and, in dense liquid deuterium, electrical insulator-to-conductor transitions associated with an increase in optical reflectivity.


In 1968, Neil Ashcroft put forward that metallic hydrogen may be a superconductor, up to room temperature (290 K or 17 °C), far higher than any other known candidate material. This stems from its expected strong coupling between the conduction electrons and the lattice vibrations.

Claimed Observation of Solid Metallic Hydrogen, 2016

On October 5, 2016, Ranga Dias and Isaac F. Silvera of the Lyman Laboratory of Physics at Harvard University released claims of experimental evidence that solid metallic hydrogen had been synthesised in the laboratory. This manuscript first appeared on the arXiv preprint server in October 2016, and a revised version was subsequently published in the journal Science in January 2017.

In the preprint version of the paper, Dias and Silvera write:

With increasing pressure we observe changes in the sample, going from transparent, to black, to a reflective metal, the latter studied at a pressure of 495 GPa... the reflectance using a Drude free electron model to determine the plasma frequency of 30.1 eV at T = 5.5 K, with a corresponding electron carrier density of 7023670000000000000♠6.7×1023 particles/cm3, consistent with theoretical estimates. The properties are those of a metal. Solid metallic hydrogen has been produced in the laboratory.

— Dias & Silvera (2016)

Shortly after the claim was published in Science, Nature's news division published an article stating that some other physicists regarded the result with skepticism, pointing out that it appears to be a matter of them testing the reflectivity of the sample at high pressure since there is a good chance it could be other factors like alumina coating used on the diamonds to prevent hydrogen from leaking into the crystal and making it brittle. Silvera stated that they did not repeat their experiment since doing more tests could damage or destroy their existing sample, but assured the scientific community that more tests are coming.

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