▎ 摘　　要

In this work, two-dimensional plasmonic crystals composed of graphene nanodisks where the chemical potential varies in triangular symmetry are proposed. A special band structure of Dirac-like cone is obtained at the center of Brillouin zone in mid-infrared region. A refractive index of the plasmons from negative to positive is calculated by the method of eigen-fields averaging. Also, the isotropic distribution of the negative/positive effective permeability and permittivity is numerically demonstrated. In addition, the significant propagation characteristics including the reverse Snell's law effect, deep-sub-wavelength focusing and negative Goos-Flanchen shifts are numerical simulated. The proposed structure may find broad applications in the fields of on-chip plasmonic interconnect, high density plasmonic integrated circuit techniques and nano-imaging in the future.