Symmetry Classification for Alternating Excitons in Two-Dimensional Altermagnets.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Excitons significantly influence the optical properties of 2D materials, revealing intrinsic characteristics like spin-orbit coupling and magnetic ordering.
• Altermagnets (AMs), a type of collinear antiferromagnet with nonrelativistic spin splitting, represent a burgeoning area of research in 2D materials.

Purpose of the Study:

• To develop a theoretical framework for elucidating excitons in 2D altermagnets (AMs) using spin space group symmetry.
• To classify exciton types and predict their optical properties and selection rules in AMs.

Main Methods:

• Utilizing a theoretical framework based on spin space group representations to classify band combinations.
• Employing effective Hamiltonians and the Bethe-Salpeter equation for detailed analysis.
• Performing first-principles calculations to predict material candidates and validate theoretical predictions.

Main Results:

• Two distinct cases of excitons (s-like and p-like) were identified in 2D AMs with spin-polarized valleys.
• Optical selection rules were determined from calculated absorption spectra and exciton symmetries.
• Several material candidates for realizing excitons in 2D AMs were predicted.

Conclusions:

• The proposed framework provides essential optical fingerprints for various altermagnet configurations.
• Tunability of excitonic properties, including strain-induced effects, was demonstrated, enabling valley-polarized photocurrent generation.