Prediction of a Mobile Solid State in Dense Hydrogen under High Pressures

Area of Science:

• Condensed Matter Physics
• Materials Science
• High-Pressure Physics

Background:

• Traditionally, solids exhibit rigidity with long-range positional order, while liquids possess fluidity and atomic mobility.
• The simultaneous existence of long-range order and liquid-scale mobility in elemental substances is considered impossible, with hypothetical exceptions like supersolid 4He.
• Understanding material behavior under extreme pressures is crucial for fundamental physics and potential technological applications.

Purpose of the Study:

• To investigate the existence of exotic states of matter in dense hydrogen under high pressure.
• To explore whether elemental substances can exhibit both solid-like positional order and liquid-like atomic mobility.
• To characterize the properties and stability of a newly discovered phase in dense hydrogen.

Main Methods:

• Utilizing ab initio molecular dynamics (AIMD) for simulating atomic interactions and behavior.
• Employing ab initio path integral molecular dynamics (AI-PIMD) to account for quantum effects, especially at lower temperatures.
• Conducting extensive simulations at pressures ranging from 1 to 1.5 TPa.

Main Results:

• Discovery of a novel state in dense hydrogen at 1-1.5 TPa possessing simultaneous long-range spatial ordering and liquid-scale atomic mobility.
• Characterization of this state's unique features, distinguishing it from conventional solids and liquids.
• Investigation into the stability and melting behavior of this exotic hydrogen phase.

Conclusions:

• The discovered state in dense hydrogen represents a classical regime example of a supersolid-like material.
• This finding challenges the conventional understanding of solid and liquid properties in elemental substances.
• The research suggests a potential new candidate for supersolid states, distinct from the known example in 4He.