Striking Isotope Effect on the Metallization Phase Lines of Liquid Hydrogen and Deuterium

August 24, 2018

A cutaway view of the structure of the planet Jupiter. Descending into the planet one transitions from gaseous hydrogen to liquid atomic hydrogen to metallic hydrogen, at high pressures and temperatures. Metallic hydrogen gives rise to the magnetic field. Jupiter may have a solid dense core. [Image credit: University of Rochester / Rodi Keisidis, Laboratory for Laser Energetics.]

Mohamed Zaghoo, Rachel J. Husband, and Isaac F. Silvera, "Striking isotope effect on the metallization phase lines of liquid hydrogen and deuterium," Physical Review B [in press].

Metallizaton of hydrogen and its isotopes has been one of the great challenging problems in condensed matter physics. There are two pathways to metallic hydrogen: very high pressure and low temperatures to make solid metallic hydrogen, or intermediate pressures (still high density) and very high temperatures (1000- 3000 K) to make liquid metallic hydrogen. In 2016, Prof. Isaac Silvera and colleagues made liquid metallic hydrogen1 and soon after solid metallic hydrogen2 in their lab. Now the physicists have measured the pressure-temperature line for the liquid molecular to liquid atomic metallic deuterium transition.3 Their measurements alleviate conflicts in the literature for the transition to liquid metallic deuterium and comparison of the hydrogen and deuterium phase lines to observe an isotope effect.

Hydrogen and deuterium are electronically identical, but the mass of deuterium is double that of hydrogen, which affects the metallization transition. The hydrogen atom has a single electron and proton; the early theory of the hydrogen atom led to the development of quantum mechanics. However, as a solid or liquid, an accurate description of the properties of hydrogen at high density have challenged theorists to develop and expand sophisticated models in which both electrons and nuclei must be treated quantum mechanically. Physics is an experimental science; the experimental phase lines provide a benchmark for theory. Thus, for example, an accurate pressure-temperature phase diagram of the transition to liquid metallic hydrogen is vital for planetary modeling. The giant outer planet Jupiter is 90% hydrogen and derives its magnetic field from the dynamo effect or motion of liquid metallic hydrogen, recently studied by the NASA Cassini and Juno probes.

Although deuterium is not a significant component of planets, it is important to have a full understanding of the hydrogen isotopes, both theoretically and experimentally. The transition line of liquid metallic deuterium was first measured and published by Sandia National Labs.4 They measured pressure (P) using dynamic shock wave techniques and calculated the temperature (T), to determine the phase line. This line was in disagreement with earlier measurements on deuterium using dynamic techniques and disagreed with recent theoretical calculations of the isotopic shif.5 We find a transition line that compares reasonably well with theory for the isotopic shift and with earlier experiments on deuterium, using static pressures generated in a diamond anvil cell in which both P and T are measured. A very recent new dynamic measurement also supports our observation.6

  1. M. M. Zaghoo, A. Salamat, and I. F. Silvera, "Evidence of a first-order phase transition to metallic hydrogen," Phys. Rev. B 93, 155128 (2016).
  2. R. Dias and I. F. Silvera, "Observation of the Wigner-Huntington Transition to Solid Metallic Hydrogen," Science 355, 715 (2017).
  3. M. Zaghoo, R. Husband, and I. F. Silvera, "Striking Isotope Effect on the Metallization Phase Lines of Liquid Hydrogen and Deuterium," Phys.Rev. B. (2018), in Press.
  4. M. D. Knudson, M. P. Desjarlais, A. Becker, R. W. Lemke, K. R. Cochrane, M. E. Savage, D. E. Bliss, T. R. Mattsson, and R. Redmer, "Direct observation of an abrupt insulator-tometal transition in dense liquid deuterium," Science 348, 1455 (2015).
  5. C. Pierleoni, M. A. Morales, G. Rillo, M. A. Strzhemechny, M. Holzmann, and D. M. Ceperley, "Liquid–liquid phase transition in hydrogen by coupled electron–ion Monte Carlo simulations," PNAS 113, 4953 (2016).
  6. P. M. Celliers et al., "Insulator-metal transition in dense fluid deuterium," Science 361, 677 (2018).