Carrier dynamics in Landau-quantized graphene featuring strong Auger scattering

• Published in: Nature physics Vol. 11; no. 1; pp. 75 - 81
• Main Authors: Mittendorff, Martin, Wendler, Florian, Malic, Ermin, Knorr, Andreas, Orlita, Milan, Potemski, Marek, Berger, Claire, de Heer, Walter A., Schneider, Harald, Helm, Manfred, Winnerl, Stephan
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2015; Nature Publishing Group
• Subjects: 140/125; 639/624/399/918; 639/766/119/995; 639/766/119/997; Atomic; Augers; Carriers; Classical and Continuum Physics; Complex Systems; Condensed Matter; Condensed Matter Physics; Depletion; Dynamics; Graphene; Ladders; Magnetic fields; Materials science; Mathematical and Computational Physics; Mesoscopic Systems and Quantum Hall Effect; Molecular; Optical and Plasma Physics; Optical pumping; Physics; Quantum physics; Scattering; Theoretical; Two dimensional
• ISSN: 1745-2473; 1745-2481; 1476-4636
• DOI: 10.1038/nphys3164

The energy spectrum of common two-dimensional electron gases consists of a harmonic (that is, equidistant) ladder of Landau levels, thus preventing the possibility of optically addressing individual transitions. In graphene, however, owing to its non-harmonic spectrum, individual levels can be addressed selectively. Here, we report a time-resolved experiment directly pumping discrete Landau levels in graphene. Energetically degenerate Landau-level transitions from n = −1 to n = 0 and from n = 0 to n = 1 are distinguished by applying circularly polarized THz light. An analysis based on a microscopic theory shows that the zeroth Landau level is actually depleted by strong Auger scattering, even though it is optically pumped at the same time. The surprisingly strong electron–electron interaction responsible for this effect is directly evidenced through a sign reversal of the pump–probe signal. Landau levels in graphene are not equidistant so that transitions between them can be individually probed. Time-resolved optical pumping experiments reveal strong electron–electron scattering resulting in an Auger-depleted zeroth order Landau level.