Circular polarization dependent cyclotron resonance in large-area graphene in ultrahigh magnetic fields

Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 $\mu$m, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular polarization dependent studies reveal strong $p$-type doping for as-grown graphene, and the dependence of the cyclotron resonance on radiation wavelength allows for a determination of the Fermi energy. Thermal annealing shifts the Fermi energy to near the Dirac point, resulting in the simultaneous appearance of hole and electron cyclotron resonance in the magnetic quantum limit, even though the sample is still $p$-type, due to graphene's linear dispersion and unique Landau level structure. These high-field studies therefore allow for a clear identification of cyclotron resonance features in large-area, low-mobility graphene samples.

Figure 1

(a) Experimental configuration for magnetotransmission using the STC magnet. (b) Magnetotransmission of 10.67-$\mu$m light through a nominally undoped CVD-grown graphene sample, during a 170 T magnet pulse. Data for both circular polarizations are shown. The pronounced CR absorption that appears for “electron-CR-inactive” polarization indicates that the graphene is $p$-type (hole doped). (c) Electron-CR-inactive transmission versus magnetic field shows two CR features at 10 T and 65 T, corresponding to $n$ = 0 to $n=-1$ and $n=-1$ to $n=-2$ inter-LL transitions.

Figure 2

(a) Wavelength-dependent electron-CR-inactive transmission traces versus magnetic field. Each trace exhibits two CR features (hole CR). (b) Landau level fan diagram with calculated LL transitions for 10.67 $\mu$m (red) and 9.22 $\mu$m (blue).

Figure 3

Wavelength-dependent electron-CR-inactive transmission traces versus the square root of magnetic field.

Figure 4

Electron-CR-inactive transmission at 10.6 $\mu$m (a) before annealing, and (b) after annealing. (c) Landau fan diagram showing the Fermi energy oscillation with magnetic field for before (blue) and after (red) annealing, and (d) depicts that annealing moves the Fermi energy from $-$295 to $-$34 meV.