Terahertz optical properties of multilayer graphene: Experimental observation of strong dependence on stacking arrangements and misorientation angles

The optical conductivity of monolayer and multilayer graphene in the terahertz spectral region is experimentally measured using terahertz time-domain spectroscopy. The stacking arrangement and the misorientation angle of each sample are determined by Raman spectroscopy. The chemical potential of each sample is measured using ultrafast midinfrared pump-probe spectroscopy to be 63 or 64 meV for all samples. The intraband scattering rate can be obtained by fitting the measured data with theoretical models. Other physical parameters, including carrier density, dc conductivity, and carrier mobility, of each sample can also be deduced from the theoretical fitting. The fitting results show the existence of misoriented or AA-stacked layers with an interaction energy of α₁=217meV in our multilayer samples. Here we show that the scattering rate strongly depends on the stacking arrangement of the sample. High scattering rates and high optical conductivity are associated with AA-stacked samples, while lower ones are associated with misoriented multilayer graphene. This implies that the THz optoelectronic properties of multilayer graphene can be tuned by purposefully misorienting layers or employing different stacking schemes.