Mechanical anisotropy and multiple direction-dependent Dirac states in a synthesized Ag3C20 monolayer

Recently, a two-dimensional (2D) orthorhombic silver-organic framework, ${\mathrm{Ag}}₃{\mathrm{C}}₂₀$ monolayer, was synthesized by assembling organic molecules linked with multiple aryl-metal bonds. Using first-principles calculation, herein we demonstrate that, owing to the unique bonding feature, ${\mathrm{Ag}}₃{\mathrm{C}}₂₀$ monolayer not only exhibits strong mechanical anisotropy, but also possesses rich orientation-dependent Dirac states allowing for modulation via external means. Around the Fermi level below, the intrinsic Dirac points form two quasi-type-III nodal lines protected by mirror symmetry, which can further evolve into hybrid nodal loops under tiny strains. Intriguingly, a peculiar semi-Dirac state near the Fermi level above emerges under a critical strain by merging two type-I Dirac cones, which harbors direction-dependent strongly localized fermions, normal massive carries, and ultrafast Dirac fermions at the same time. These findings suggest that the mechanically sensitive ${\mathrm{Ag}}₃{\mathrm{C}}₂₀$ monolayer is a promising 2D material to realize the interesting Dirac physics and multiple carrier transport with high anisotropy.