  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.

Materials Science;Computational Physics