Band-Geometry-Driven Spin Photocurrent in Centrosymmetric Altermagnets

Area of Science:

• Condensed Matter Physics
• Spintronics
• Quantum Geometry

Background:

• Geometric responses of Bloch states are key to charge and spin transport in solids.
• The geometry of Hamiltonian eigenvalues is typically considered trivial.
• Altermagnets are a new class of magnetic materials with unique symmetry properties.

Purpose of the Study:

• To investigate the role of Hamiltonian eigenvalue geometry in spin transport.
• To explore spin current generation in centrosymmetric altermagnets.
• To identify mechanisms for switchable spin transport without charge flow.

Main Methods:

• Quantum perturbation theory applied to optical excitation and static electric fields.
• Symmetry-based analysis of centrosymmetric spin point groups.
• First-principles calculations on α-MnTe and MnF_{2}.

Main Results:

• The geometry of Hamiltonian eigenvalues can generate transverse spin currents in altermagnets.
• Two leading mechanisms, effective-mass and group-velocity terms, are identified, linked to band geometry.
• These mechanisms enable selective and switchable spin transport without charge flow, independent of inversion symmetry breaking.
• Predicted spin conductivities are experimentally accessible under moderate fields.

Conclusions:

• The seemingly trivial geometry of Hamiltonian eigenvalues plays a significant role in spin transport.
• Centrosymmetric altermagnets offer a platform for novel spintronic phenomena.
• The findings pave the way for designing materials with controlled spin currents.