Spin-Selective Second-Order Topological Insulators Enabling Cornertronics in Two-Dimensional Altermagnets.

Recent progress in spintronics within the paradigm of altermagnets (AMs) opens new avenues for next-generation electronic device design. Here, we establish a spin-corner locking mechanism that generates second-order topological states in two-dimensional (2D) altermagnetic systems through effective model analysis. Remarkably, the breaking of M_xy symmetry under uniaxial strain creates spin-resolved corner modes, driving the system into a corner-polarized second-order topological insulator (CPSOTI). Beyond critical strain, a topological phase transition to a quantum anomalous Hall insulator occurs with quantized conductance. Through first-principles calculations, we identify two experimentally viable candidates for 2D intrinsic AM CrO and Cr₂Se₂O, which host robust CPSOTI. Moreover, we construct the topological phase diagram of CrO and predict the existence of an altermagnetic Weyl semimetal phase. Our findings open technological avenues in altermagnetism and higher order topology while providing opportunities for coupling topological spintronics with cornertronics.