Dirac fermions in the altermagnet Ce4Sb3

Altermagnetism exhibits zero net magnetization and spin-splitting electronic structure. The interplay between altermagnetism and topological physics becomes an important topic in condensed matter physics. In this work, we propose that the altermagnet ${\mathrm{Ce}}_{4}{\mathrm{Sb}}_{3}$ hosts Dirac fermions and we explore this idea through first-principles calculations and tight-binding-model analysis. When subjected to an external magnetic field, the altermagnet ${\mathrm{Ce}}_{4}{\mathrm{Sb}}_{3}$ changes from an altermagnetic state to a ferromagnetic state. Accompanied by magnetic order transition, the fourfold degenerate Dirac points transit into sextuple degenerate points. Especially, the spin-orbit-coupling effect has little influence on the Dirac fermions. The topological phases in the altermagnetic state may hold the exotic spin-splitter torque and the remarkable nonlinear transport effect. Our work paves the way for exploring the interplay between altermagnetism and the nontrivial topological phase.