Stacking-, strain-engineering induced altermagnetism, multipiezo effect, and topological state in two-dimensional materials

Altermagnetism, a recently identified form of unconventional antiferromagnetism (AFM), enables the removal of spin degeneracy in the absence of net magnetization that provides a platform for the low power consumption and ultra-fast device applications. However, a little attention has been paid to the relationship between stacking, strain, and altermagnet, the multipiezo effect, and the topological state. Here, we propose a mechanism to realize the altermagnet, the multipiezo effect, and the topological state in two-dimensional (2D) materials by the stacking and strain engineering. Based on the analysis of symmetry, we find that the spin splitting feature related to the Ut, PTt, MzUt, or MzPTt symmetries in altermagnet multilayers. In addition, we find that the stacking engineering can effectively realize the transform from antiferromagnetism to altermagnetism and semiconductor to metal for the Janus bilayer V2SeTeO. More interestingly, the strain not only induces an intriguing multipiezo effect, encompassing the piezovalley, piezomagnetism, and piezoelectric, but also achieves the abundant topological phase. Our findings offer a generalized direction for manipulating the spin splitting, valley polarization, and topological states, promoting practical application of valleytronic and spintronic devices based on two-dimensional altermagnets.