Giant valley splitting in monolayer HfN2 induced by magnetic doping

Monolayer HfN2 (HfN2-ML) is a promising valleytronic material; however, its valley degeneracy is preserved by time-reversal symmetry (TRS), prohibiting net valley Hall currents. Herein, we systematically explore the electronic structures, valley polarization, and transport properties of pristine and Mn-doped HfN2-ML via first-principles calculations coupled with band-unfolding techniques. Our calculations verify that Mn substitution breaks spatial inversion symmetry and generates local magnetic moments that lift TRS. Band-unfolding calculations yield a giant valley splitting of 107.6 meV at the conduction band minimum, whereas valley splitting at the valence band is negligible. The formed valley polarization is further evidenced by nonzero valley Hall conductivity. These results identify Mn-doped HfN2 as an attractive candidate toward room-temperature valleytronic devices and shed light on the rational design of nitride-based functional materials.