Metallic Hydrogen: A Liquid Superconductor?

TL;DR

This study investigates the potential for liquid metallic hydrogen to be a superconductor, using first-principles simulations and Eliashberg equations, suggesting liquid hydrogen could indeed exhibit superconductivity at high pressures.

Contribution

The paper provides the first theoretical evidence that liquid atomic hydrogen can be superconducting, identifying specific pressure and temperature conditions for its existence.

Findings

Superconducting critical temperature (Tc) ranges from 308K to 372K under high pressures.

Tc is similar in both solid and liquid phases despite different underlying physics.

Liquid hydrogen is predicted to be a superconducting state at certain high-pressure conditions.

Abstract

Metallic hydrogen is expected to exhibit remarkable physics. Of particular interest in this work is the possibility of high-temperature superconductivity. Comparing calculations of the superconducting critical temperatures of the solid phase to melting temperatures over a range of pressures leads to an interesting question: Will the solid, in a superconducting state, melt to a liquid that remains a superconductor? In this work, the possibility of liquid superconductivity in metallic hydrogen is investigated. This is done by first-principles simulations, and using the results of these to solve the Eliashberg equations. These are carried out over the pressure (and temperature) conditions where molecular dissociation is expected to first occur in the solid phase. Over the pressure range $386.8(4)$--$783.7(4)$ GPa, $T_c$ increases from $308(6)$ to $372(2)$ K with a maximum uncertainty of $10$ K; it then decreases to $356(2)$ K at $883.7(3)$ GPa. Comparisons to the solid phase show that the critical temperature is not significantly changed between the two phases, though the physics behind their superconductivity is different. Careful comparisons of these values to recent results in the context of the hydrogen phase diagram show that they are higher than the melting temperatures and that the solid will melt to liquid atomic hydrogen. The results of this work (in this context) therefore suggest that liquid atomic hydrogen will indeed exist in a superconducting state. They also provide the pressure and temperature conditions over which to look for it.