Low temperature phase diagram of hydrogen at pressures up to 380 GPa. A possible metallic phase at 360 GPa and 200 K

TL;DR

This study maps the low-temperature phase diagram of hydrogen up to 380 GPa, discovering a potentially metallic phase at 360 GPa and 200 K through spectroscopic and electrical measurements.

Contribution

It reports the discovery of a new phase VI of hydrogen at high pressure and low temperature, suggesting metallic properties, and constructs an updated phase diagram.

Findings

Discovery of phase VI at ~360 GPa and <200 K

Evidence of metallic behavior in phase VI from resistance and spectra

Updated hydrogen phase diagram up to 380 GPa

Abstract

Two new phases of hydrogen have been discovered at room temperature in Ref.1: phase IV above 220 GPa and phase V above ~270 GPa. In the present work we have found a new phase VI at P~360 GPa and T<200 K. This phase is likely metallic as follows from the featureless Raman spectra, a strong drop in resistance, and absence of a photoconductive response. We studied hydrogen at low temperatures with the aid of Raman, infrared absorption, and electrical measurements at pressures up to 380 GPa, and have built a new phase diagram of hydrogen.