Altermagnetism and higher-order topological states in bilayer Chern insulators

We propose an innovative strategy to integrate $d$-wave altermagnetism with intrinsic second-order topological phases in two-dimensional bilayer Chern insulators. Using bilayer ${\mathrm{V}}_{2}{\mathrm{WS}}_{4}$ as a case study, our first-principles calculations reveal that the A-type antiferromagnetic interlayer configuration transforms the system into a $d$-wave altermagnet, resulting in four topological corner states localized at the corners of a square flake. Notably, interlayer sliding disrupts the symmetry between diagonal and antidiagonal corners, leading to a controlled splitting of the corner state into two doubly degenerate sets. An effective lattice model successfully captures the essential features observed in our first-principles calculations, providing insights into the interplay between stacking geometry, interlayer interactions, and higher-order topology. Our findings position $d$-wave altermagnets as a promising platform for engineering tunable higher-order topological states, paving the way for their integration into van der Waals heterostructures.