Magneto-infrared spectroscopy of nonpolar epigraphene

We report on a magneto-infrared spectroscopy study of the new generation epigraphene grown on a nonpolar facet of SiC. We observe interband Landau level (LL) transitions that can be well described by a massless Dirac fermion model with a Fermi velocity of 1 x 10⁶ m/s. The transitions remain visible as the magnetic field is down to 0.25 T, indicating that the carrier density is no greater than 3.6 x 10¹⁰ cm^-2 as expected for charge-neutral nonpolar epigraphene. When the samples are grown thicker, LL transition splittings are spotted at high magnetic fields. Failing to explain the splittings with electron-hole asymmetry, we suggest that it could arise from the (twist) bilayer epigraphene components, which we will discuss with a numerical twist-bilayer model.