Expanded Comment on: Optical Properties of Fluid Hydrogen at the Transition to a Conducting State

TL;DR

This paper critiques a recent claim that high-pressure hydrogen is semi-conducting, highlighting inconsistencies with prior metallic hydrogen observations and proposing an alternative interpretation consistent with metallic behavior.

Contribution

It provides a critical analysis of recent experimental claims and offers an alternative interpretation supporting metallic hydrogen at high pressures.

Findings

Identifies inconsistencies in recent semi-conducting claims

Proposes an interpretation compatible with metallic hydrogen

Reinforces previous evidence of metallic behavior in hydrogen

Abstract

We comment on a recent paper published by McWilliams et al claiming that high-pressure/high-temperature hydrogen is a semi-conductor or semi-metal, in conflict with all earlier measurements on this system which show that it is metallic. We point out problems and inconsistencies and propose an alternate interpretation such that their results can be compatible with the observation of metallic hydrogen.