Isaac F. Silvera

Isaac F. Silvera

Thomas D. Cabot Professor of the Natural Sciences
Isaac Silvera

 

Isaac Silvera's research is in both condensed matter and physics of cold particles. His current interests are in ultra-high pressure and low-temperature physics of quantum fluids.

Over 70 years ago Wigner and Huntington predicted that at a high pressure of a 0.25 megabar, solid molecular hydrogen would become an atomic metal. Theoretical predictions that it might be a liquid at low temperatures due to its large zero-point energy, a room temperature superconductor, superfluidity, etc. spurred the effort to produce this in the laboratory. It had also been predicted that metallic hydrogen (MH) might be metastable, i.e. remain metallic when the pressure was lifted. It was also predicted that at pressures of order 1-2 megabars, if hydrogen was heated to temperatures of thousands of degrees, the solid would melt to a molecular liquid and with increasing temperature the molecules dissociate to form liquid atomic metallic hydrogen.  In 2016-2017 we succeeded to observe the Wigner-Huntington transition to atomic metallic hydrogen in the laboratory at a pressure of almost 5 megabars (500 GPa) and low temperatures. We observed the high temperature liquid-liquid phase transition a few years earlier. To generate the high-pressure we use diamond anvil cells to compress samples to high pressures at extreme temperatures.  Most studies of the properties are carried out by optical techniques.

The research focus is on hydrogen and its isotopes, deuterium and HD, with an effort to produce and study metallic phases. With increasing pressure the molecular hydrogen isotopes undergo a number of phase transitions. New phases of orientational order called the broken symmetry phase and an as yet uncharacterized phase called the hydrogen-A phase at pressures above 1.5 megabar have been discovered. Techniques involve Raman scattering, IR spectroscopy, pulsed laser heating, NMR, equation of state measurements, conductivity, synchrotron x-ray studies, etc. Recent developments in the area of pulsed laser heating of samples use short, high-power pulses at infrared wavelengths; samples can be heated to several thousand degrees K. The melting line was studied and found to have a maximum with increasing pressure.

In a recent experiment we have shown that low temperature MH is not metastable. Currently studies are being carried out to study superconductivity in hydrogen and to extend such studies to  deuterium and HD.

 

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Faculty Assistant: Meghan McDaid

 

Contact Information

Lyman Lab 224
17 Oxford Street
Cambridge, MA 02138
p: (617) 495-9075