Ferroelectric Generation and Switching of the Hidden Altermagnetism in Parity-Time-Structured Multiferroic CuCrP2S6.

The electrical control of altermagnetic spin splitting represents a critical ability to engineer band landscapes for generating emergent magnetoelectric physics and spintronic applications. Previous efforts have mainly resorted to hypothetical ferroelectric-altermagnetic materials to integrate ferroelectricity and altermagnetism into one system. However, even with such integration, the even-parity nature of altermagnetic band structures usually impedes the realization of ferroelectric-switchable altermagnetism, as polarization switching is widely assumed to be a spatial parity transformation. Here, we report the ferroelectric-switchable altermagnetism in an experimentally accessible van der Waals crystal CuCrP2S6, whose ground state has long been deemed to be an antiferroelectric-antiferromagnet. Driven by parity-time (PT) symmetry breaking through metastable ferroelectricity, bulk CuCrP2S6 instead transitions to a d-wave altermagnet. Despite its breaking, the PT symmetry remains operative as a transformation associated with polarization switching, underpinning the ferroelectric-switchable altermagnetism in bulk CuCrP2S6. Our theoretical findings elucidate a general symmetry-engineering strategy for ferroelectric-switchable altermagnetism.