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Physicists Produce World’s First Sample of Metallic Hydrogen

A duo of physicists at Harvard University has succeeded in creating a metallic modification of hydrogen. The research is published in the journal Science.

Photo of metallic hydrogen at a pressure of 495 GPa; the sample is non-transmitting and is observed in reflected light; the central region is clearly more reflective than the surrounding metallic rhenium gasket; the sample dimensions are approximately 8-10 microns with thickness 1.2 microns. Image credit: Ranga P. Dias  Isaac F. Silvera, doi: 10.1126/science.aal1579.

Photo of metallic hydrogen at a pressure of 495 GPa; the sample is non-transmitting and is observed in reflected light; the central region is clearly more reflective than the surrounding metallic rhenium gasket; the sample dimensions are approximately 8-10 microns with thickness 1.2 microns. Image credit: Ranga P. Dias Isaac F. Silvera, doi: 10.1126/science.aal1579.

Originally theorized by Princeton physicists Eugene Wigner and Hillard Bell Huntington in 1935, metallic hydrogen is ‘the holy grail of high-pressure physics.’

Theoretical work suggests a wide array of interesting properties for this material, including high temperature superconductivity and superfluidity (if a liquid).

To create it, Harvard University physicists Dr. Ranga Dias and Professor Isaac Silvera squeezed a tiny hydrogen sample at 495 GPa (gigapascal) — greater than the pressure at the center of the Earth.

At those extreme pressures, solid molecular hydrogen -which consists of molecules on the lattice sites of the solid – breaks down, and the tightly bound molecules dissociate to transforms into atomic hydrogen, which is a metal.

“We have studied solid molecular hydrogen under pressure at low temperatures,” the researchers said.

“At a pressure of 495 GPa hydrogen becomes metallic with reflectivity as high as 0.91.”

“We fit the reflectance using a Drude free electron model to determine the plasma frequency of 32.5 ± 2.1 eV at T = 5.5 K, with a corresponding electron carrier density of 7.7 ± 1.1 × 1023 particles/cm3, consistent with theoretical estimates of the atomic density.”

“The properties are those of an atomic metal,” they noted.

To create the material, the authors turned to one of the hardest materials on Earth — diamond.

But rather than natural diamond, they used two small pieces of carefully polished synthetic diamond which were then treated to make them even tougher and then mounted opposite each other in a device known as a diamond anvil cell.

“It was really exciting,” Professor Silvera said.

“Ranga was running the experiment, and we thought we might get there, but when he called me and said, ‘The sample is shining.’ I went running down there, and it was metallic hydrogen.”

“I immediately said we have to make the measurements to confirm it, so we rearranged the lab, and that’s what we did.”

“It’s a tremendous achievement, and even if it only exists in this diamond anvil cell at high pressure, it’s a very fundamental and transformative discovery.”

While the work offers a new window into understanding the general properties of hydrogen, it also offers tantalizing hints at potentially revolutionary new materials.

“One prediction that’s very important is metallic hydrogen is predicted to be meta-stable,” Professor Silvera explained.

“That means if you take the pressure off, it will stay metallic, similar to the way diamonds form from graphite under intense heat and pressure, but remains a diamond when that pressure and heat is removed.”

“Metallic hydrogen may have important impact on physics and perhaps will ultimately find wide technological application,” the researchers said.

“A looming challenge is to quench metallic hydrogen and if so study its temperature stability to see if there is a pathway for production in large quantities.”

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Ranga P. Dias Isaac F. Silvera. Observation of the Wigner-Huntington transition to metallic hydrogen. Science, published online January 26, 2017; doi: 10.1126/science.aal1579