Mechanical Anisotropy and Multiple Direction-Dependent Dirac States in the Synthesized Ag3C20 Monolayer

Recently, a 2D orthorhombic silver-organic framework, Ag3C20 monolayer, was synthesized by assembling organic molecules linked with multiple aryl-metal bonds. Herein, via first-principles study, we demonstrate that owing to the unique bonding feature, Ag3C20 monolayer not only exhibits strong mechanical anisotropy, but also possesses various tunable direction-dependent Dirac states. Around the Fermi level blow, the intrinsic Dirac points form two antiparallel quasi type-III nodal lines protected by mirror symmetry, which can further evolve into hybrid nodal loops under tiny strains. Intriguingly, near the Fermi level above, a special semi-Dirac state can emerge under a critical strain by merging two type-I Dirac cone, 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 Ag3C20 monolayer is a promising 2D material to realize the interesting Dirac physics and highly anisotropic multiple carries transport.