Strain-induced phase transition from antiferromagnet to altermagnet

The newly discovered altermagnets are unconventional collinear compensated magnetic systems, exhibiting even (d, g, or i wave) spin-polarization order in the band structure, setting them apart from conventional collinear ferromagnets and antiferromagnets. Altermagnets offer advantages of spin-polarized current akin to ferromagnets, and THz functionalities similar to antiferromagnets, while introducing new effects like spin-splitter currents. A key challenge for future applications and functionalization of altermagnets is to demonstrate controlled transitioning to the altermagnetic phase from other conventional phases in a single material. Here we prove a viable path toward overcoming this challenge through a strain-induced transition from an antiferromagnetic to an altermagnetic phase in ReO₂. Combining spin group symmetry analysis and ab initio calculations, we demonstrate that under compressive strain ReO₂ undergoes such transition, lifting the Kramers degeneracy of the band structure of the antiferromagnetic phase in the nonrelativistic regime. In addition, we show that this magnetic transition is accompanied by a metal-insulator transition, and calculate the distinct spin-polarized spectral functions of the two phases, which can be detected in angle-resolved photoemission spectroscopy experiments.