Structure and Metallicity of Phase V of Hydrogen - Drs. Philip Dalladay-Simpson, Ross T. Howie, and Eugene Gregoryanz

JUNE 18, 2018

A new study from a team of scientists, which comprised of HPSTAR’s Philip Dalladay-Simpson, Ross T. Howie, and Eugene Gregoryanz, proposed a promising candidate crystal structure for their recently discovered phase of hydrogen, phase V. Most poignantly the work,  which was recently published Physical Review Letters,  provides further evidence that phase V is indeed a stepping stone towards hydrogen’s elusive metallic form.

Metallic hydrogen is a longstanding topic in the field of condensed matter of physics since its prediction over 80 years ago. Since, this state of matter has been suggested to exhibit exotic  dissapationless states of matter at high temperatures, such as superconductivity and superfluidity.  However, in these regimes, complete characterisation of hydrogen is difficult as experimentalists become diagnostically poor, previously only finding Raman spectroscopy as a suitable probe. Fortunately, hydrogen has exceedingly rich vibrational properties and in this study, through the interplay of new theoretical techniques and experimental observation it is possible to ascertain the first structural knowledge of phase V.

In this study, the team used a newly developed saddle-point ab initio random structure searching methods (sp-AIRSS), to find candidate model crystal structures for phase V, reporting three new   structures which suitably describe the characteristics for phase V. Interestingly, the study proposed that the structure with the longer bond lengths and the smallest band gap, as the most promising model structure for hydrogen phase V. Noteworthy, as both these properties reflect the continuous metallisation and onset of dissociation in the hydrogen system, corroborating the previous experimental results on phase V.

“It is exciting that our newly discovered phase V, a phase exhibiting marked changes, has finally found a working model”, said Dr. Dalladay Simpson, one of the co-authors and a staff scientist at HPSTAR.  “This study is integral to answering the longstanding standing questions regarding the emergence of metallic hydrogen in a condensed form.”