Mirror-symmetry-protected Dirac nodal lines and rings in two-dimensional P2/m-B11 borophene

The exploration of stable two-dimensional Dirac nodal-line materials is essential for understanding and realizing low-dimensional topological quantum states. Here, using first-principles calculations and symmetry analysis, we predict a novel borophene allotrope, P2/m-B11, and systematically investigate its structural stability and electronic properties. Phonon calculations and ab initio molecular dynamics simulations confirm its excellent dynamical and thermal stability. Remarkably, P2/m-B11 borophene hosts two Dirac nodal lines and two Dirac nodal rings in the vicinity of the Fermi level, arising from linear Dirac band crossings. The corresponding Fermi velocities are comparable to those of graphene, implying potentially high carrier mobility. Symmetry analysis reveals that these nodal features are protected by mirror symmetry. Owing to the weak intrinsic spin–orbit interaction of boron, they remain nearly intact in the presence of spin–orbit coupling. These findings establish P2/m-B11 borophene as a promising two-dimensional nodal-line semimetal and provide a viable borophene platform for exploring topological quantum phenomena and next-generation electronic devices.