Alter-Piezoresponse in Two-Dimensional Lieb-Lattice Altermagnets

Altermagnetism, featuring alternating spin structures in reciprocal space, has sparked growing interest. Here, we predict novel real-space alternative piezomagnetic and piezoelectric responses in an emerging altermagnetic family of Lieb lattices, specifically transition-metal chalcogenides M2WS4 (M = Mn, Fe, Co). The unique S4T crystal-spin symmetry leads to distinct magnetic and electric responses depending on the direction of applied stress. When subjected to axial stress, they exhibit a giant piezomagnetic response, which is about one to two orders of magnitude larger than that of most piezomagnetic materials, while the residual C2 symmetry suppresses the piezoelectric effect. In contrast, diagonal stress induces an imbalance of oppositely aligned electric dipole moments and a significant piezoelectric response, while in-plane mirror symmetry inhibits the piezomagnetic effect. This alternative piezoresponse offers an unprecedented opportunity to precisely control electric and magnetic properties independently, opening new avenues for altermagnetic materials in high-fidelity multifunctional memory and sensor applications.