Altermagnetism-induced iron-based third-order topological superconductivity

We theoretically demonstrate that a three-dimensional third-order topological superconductor, i.e., Majorana corner states, can be engineered by introducing $d$-wave altermagnetism into iron-based $({s}_{\ifmmode\pm\else\textpm\fi{}}\text{\ensuremath{-}}\mathrm{wave})$ superconductors. We find that the interplay between altermagnetism and iron-based superconductivity gives rise to mass domain walls at the corners, leading to the emergence of Majorana zero modes. We further calculate the nonzero mirror-graded winding number to characterize the third-order phases of the system. In the end, we show that the distribution of Majorana zero modes can be spatially manipulated by tuning the N\'eel vector of the altermagnet.