Spin—orbit stable dirac nodal line in monolayer B₆O

The two-dimensional (2D) materials with nodal line band crossing have been attracting great research interest. However, it remains a challenge to find high-stable nodal line structure in 2D systems. Herein, based on the first-principles calculations and theoretical analysis, we propose that monolayer B₆O possesses symmetry protected Dirac nodal line (DNL) state, with its Fermi velocity of 10⁶ m/s in the same order of magnitude as that of graphene. The origin of DNL fermions is induced by coexistence of time-reversal symmetry and inversion symmetry. A two-band tight-binding model is further given to understand the mechanism of DNL. Considering its robustness against spin—orbit coupling (SOC) and high structural stability, these results suggest monolayer B₆O as a new platform for realizing future high-speed low-dissipation devices.