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

Abstract 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.