d-Wave Flat Fermi Surface in Altermagnets Enables Maximum Charge-to-Spin Conversion

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Altermagnets exhibit unique antiferromagnetic and ferromagnet-like properties, enabling ultrafast spin-dependent responses.
• Conventional spin-transfer and spin-orbit torque methods face limitations in magnetic memory technologies.
• Understanding spin-current generation in altermagnets is crucial for next-generation spintronics.

Purpose of the Study:

• To establish a fundamental relationship between Fermi surface geometry and time-reversal-odd (T-odd) spin currents in altermagnets.
• To explore the potential of altermagnets for efficient spin-current generation.
• To investigate the charge-to-spin conversion efficiency (CSE) in a novel room-temperature altermagnet.

Main Methods:

• Combined model analysis and first-principles calculations were employed.
• Investigation focused on d-wave altermagnets with flat Fermi surfaces.
• Experimental characterization of the newly discovered KV2Se2O altermagnet.

Main Results:

• A theoretical charge-to-spin conversion efficiency (CSE) of 100% was demonstrated for d-wave altermagnets with flat Fermi surfaces.
• The room-temperature altermagnetic metal KV2Se2O achieved a record T-odd CSE of ~78% at the charge neutrality point.
• Electron doping in KV2Se2O further increased CSE to ~98%, approaching the theoretical limit.

Conclusions:

• Fermi surface geometry engineering is a key factor in controlling T-odd spin currents in altermagnets.
• KV2Se2O represents a significant advancement in altermagnetic materials for spintronics.
• This research provides critical insights for developing high-performance altermagnet-based memory devices.