Gapless Criterion for Crystals from Effective Axion Field.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Crystallography

Background:

• Identifying topological semimetals is crucial for advanced electronic applications.
• Existing methods for detecting gapless phases in crystals can be limited.
• Topological semimetals possess unique electronic properties due to their band structure.

Purpose of the Study:

• To propose a novel and efficient gapless criterion for three-dimensional noninteracting crystals.
• To provide a new tool for the discovery of topological semimetals.
• To overcome limitations of current symmetry-based detection methods.

Main Methods:

• Derivation of a sufficient gapless criterion based on simplified static axion field expressions.
• Application of the criterion to magnetic systems with specific space groups (26 and 13).
• Comparison with the symmetry-representation approach for gapless phase identification.

Main Results:

• A new gapless criterion was successfully proposed and validated.
• The criterion effectively identifies gapless phases in magnetic crystals.
• The method detected gapless phases missed by the symmetry-representation approach, particularly in space group 26.

Conclusions:

• The proposed gapless criterion is a powerful tool for identifying topological semimetals.
• This method offers a guiding principle for future discoveries in topological materials.
• The criterion enhances the efficiency and scope of gapless phase detection in crystals.