Topological characteristics and anomalous transport in CoRhMnSi and CoRhMnGe quaternary Heusler alloys.

Magnetic Weyl semimetals (WSMs) represent a significant class of topological quantum materials characterized by nondegenerate band-touching points, known as Weyl nodes. A hallmark feature of these systems is the existence of symmetry-protected surface Fermi arcs that link Weyl nodes of opposite chirality within the surface Brillouin zone. In this work, we present a systematic first-principles study of the electronic, magnetic, topological, and anomalous transport properties of CoRhMnSi and CoRhMnGe, quaternary Heusler alloys. Spin-polarized electronic band structure calculations confirm a ferromagnetic ground state and half-metallic nature in both compounds. The topological characteristics are explored through a tight-binding approach based on Wannier functions incorporating spin-orbit coupling, which reveals the presence of multiple Weyl nodes with opposite chirality. The observation of robust, symmetry-protected surface Fermi arcs provides compelling evidence for Weyl semi-metallic behaviour in these materials. In addition, we evaluate the anomalous transport responses along the [001] crystallographic direction and obtain large anomalous Hall conductivities of -706.34 and -1300.29 S cm-1 for CoRhMnSi and CoRhMnGe, respectively, at 0 K. Correspondingly, significant anomalous Nernst conductivities of -4.55 and -4.75 A m-1 K-1 are predicted at room temperature, exceeding those reported for several other Co-based magnetic Heusler alloys. These findings highlight a strong interplay between band topology and anomalous transport phenomena in these Heusler alloys, underscoring their potential for spintronic and thermoelectric applications.