Topological Surface States in Dense Solid Hydrogen

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Metallization of dense hydrogen is a key problem in physics, potentially leading to high-temperature superconductivity.
• Theoretical studies suggest hydrogen transitions through a semimetallic phase before full metallization.
• Understanding these intermediate phases is crucial for predicting hydrogen's properties under extreme pressure.

Purpose of the Study:

• To investigate the electronic properties of semimetallic phases in dense hydrogen.
• To determine if these phases exhibit conventional or unconventional semimetallic behavior.
• To identify potential mechanisms for superconductivity in compressed hydrogen.

Main Methods:

• First-principles calculations were used to model dense hydrogen phases.
• Electronic band structures were analyzed to identify metallic and semimetallic characteristics.
• Topological properties of the electronic states were examined.

Main Results:

• Stable semimetallic phases of dense hydrogen (e.g., Cmca-12, Cmca-4) were identified at multimegabar pressures.
• These phases exhibit topological metallic surface states within the bulk band gap.
• Pbcn hydrogen also shows metallic surface states, but they are non-topological in nature.

Conclusions:

• Dense hydrogen can possess topological metallic surface states, distinct from conventional semimetals.
• These surface states may enable superconductivity even when the bulk remains insulating.
• The findings provide predictions for experimental verification of surface superconductivity in dense hydrogen.