A metallic room-temperature d-wave altermagnet

Abstract

Altermagnetism is a recently discovered unconventional magnetic phase that is characterized by time-reversal symmetry breaking and spin-split band structures in materials with zero net magnetization. Recently, spin-polarized band structures and a vanishing net magnetization were observed in semiconductors MnTe and MnTe₂, confirming this unconventional magnetic order. Metallic altermagnets offer advantages for exploring physical phenomena related to low-energy quasiparticle excitations and for applications in spintronics because the finite electrical conductivity of metals allows direct manipulation of the spin current through the electric field. We demonstrate that KV₂Se₂O is a metallic room-temperature altermagnet with d-wave spin-momentum locking. Our experiments probe the magnetic and electronic structures of this compound and reveal a highly anisotropic spin-polarized Fermi surface and the emergence of a spin-density-wave order in the altermagnetic phase. These characteristics suggest that KV₂Se₂O could be a helpful platform for high-performance spintronic devices and for studying many-body effects coupled with unconventional magnetism.