Hydrogen Deuteride: New Phases and Unexpected Behavior
Hydrogen and its isotopes, deuterium and hydrogen deuteride (HD), are the simplest and most abundant elements in the universe. At a sufficient pressure the solids are predicted to dissociate into atoms and become metallic with possible room temperature superconductivity.
Prof. Isaac Silvera and postdocs Ranga Dias and Ori Noked have studied HD to its highest pressure ever, 3.4 million atmospheres, in a diamond anvil cell compressed by more than a factor of 10 in volume. This is about the pressure at the center of the Earth. At this pressure regime the team observed two new phases, starting at the low temperature (T=0 Kelvin) limit. They found HD to be a stable molecule in the solid up to 2 million atmospheres, when the first new phase is entered and the molecules dissociate. Unfortunately, this is not the long sought transition to metallic H and D. Neighboring molecules in the solid rapidly dissociate and recombine to form new molecules of molecular hydrogen and deuterium, identified by their infrared spectra, leaving a mixed isotopic solid. The authors named this process DISREC for dissociation-recombination. The highest pressure new phase has been named HD-PRE as it may just precede the transition to the metallic phase.
The paper will appear in Physical Review Letters: Ranga P. Dias, Ori Noked, and Isaac F. Silvera, "Hydrogen Deuteride: New Phases and unexpected behavior when pressed to 3.4 million atmospheres," PRL 116, 145501 (2016).
See also phys.org, "Pressing the Simplest Element to Exotic Quantum States."
Phase diagram of hydrogen deuteride