Electronic excitations in doped monolayer graphenes

The energy dispersions and the electronic excitations of doped monolayer graphenes are, respectively, calculated from the tight-binding model and the random phase approximation. The special features of excitation spectra are dominated by the Fermi energy, the band structure, the doping type, and the transferred momentum (q). Doping would induce free carriers, which further cause the intraband single-particle and collective excitations. Due to the band asymmetry of about E_F =0, the low-frequency excitation spectra exhibit a huge difference between the electron and hole doping. The hole doping causes the excitations with lower frequency, and one intraband and interband plasmon changes into one intraband plasmon and one interband plasmon at certain q. However, the high-frequency excitations are independent of the Fermi energy and the doping type. The excitation properties extremely differ from those of the band symmetry systems. The main differences, caused by the band symmetry and the Fermi energy, include the consistency of spectra among the ± E _F, the plasmon peak number in the hole doping, and the q dependence of plasmon frequency.