Tunable two-dimensional Dirac-Weyl semimetal phase induced by altermagnetism

We demonstrate a tunable Dirac-Weyl semimetal phase in two dimensions, realized by introducing in-plane $d$-wave altermagnetism into a Dirac system. This phase hosts both a central Dirac point and momentum-separated Weyl points connected by Fermi line edge states. The Weyl point positions---and thus the edge-state connectivity---can be continuously tuned by rotating the altermagnetic axis. In contrast, out-of-plane altermagnetism gaps part of the bulk spectrum while preserving a single Dirac point accompanied by chiral edge modes, as evidenced by quantized edge polarization. Our findings provide a tunable platform for manipulating Dirac-Weyl physics and topological edge transport in two dimensions.