Efficient Auger scattering in Landau-quantized graphene

We present an analytical expression for the differential transmission of a delta-shaped light field in Landauquantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene

Ultra-large polymer-free suspended graphene films

Due to its extraordinary properties, suspended graphene is a critical element in a wide range of applications. Preparation methods that preserve the unique properties of graphene are therefore in high demand. To date, all protocols for the production of large graphene films have relied on the application of a polymer film to stabilize graphene during the transfer process. However, this inevitably introduces contaminations that have proven to be extremely difficult, if not impossible, to remove entirely. Here we report the polymer-free fabrication of suspended films consisting of three graphene layers spanning circular holes of 150 $\mu$m diameter. We find a high fabrication yield, very uniform properties of the freestanding graphene across all holes as well across individual holes. A detailed analysis by confocal Raman and THz spectroscopy reveals that the triple-layer samples exhibit structural and electronic properties similar to those of monolayer graphene. We demonstrate their usability as ion-electron converters in time-of-flight mass spectrometry and related applications. They are two orders of magnitude thinner than previous carbon foils typically used in these types of experiments, while still being robust and exhibiting a sufficiently high electron yield. These results are an important step towards replacing free-standing ultra-thin carbon films or graphene from polymer-based transfers with much better defined and clean graphene.Comment: 9 pagers, 5 figure

Slow Noncollinear Coulomb Scattering in the Vicinity of the Dirac Point in Graphene

The Coulomb scattering dynamics in graphene in energetic proximity to the Dirac point is investigated by polarization resolved pump-probe spectroscopy and microscopic theory. Collinear Coulomb scattering rapidly thermalizes the carrier distribution in k directions pointing radially away from the Dirac point. Our study reveals, however, that, in almost intrinsic graphene, full thermalization in all directions relying on noncollinear scattering is much slower. For low photon energies, carrier-optical-phonon processes are strongly suppressed and Coulomb mediated noncollinear scattering is remarkably slow, namely on a ps time scale. This effect is very promising for infrared and THz devices based on hot carrier effects

Strong transient magnetic fields induced by THz-driven plasmons in graphene disks

Strong circularly polarized excitation opens up the possibility to generate and control effective magnetic fields in solid state systems, e.g., via the optical inverse Faraday effect or the phonon inverse Faraday effect. While these effects rely on material properties that can be tailored only to a limited degree, plasmonic resonances can be fully controlled by choosing proper dimensions and carrier concentrations. Plasmon resonances provide new degrees of freedom that can be used to tune or enhance the light-induced magnetic field in engineered metamaterials. Here we employ graphene disks to demonstrate light-induced transient magnetic fields from a plasmonic circular current with extremely high efficiency. The effective magnetic field at the plasmon resonance frequency of the graphene disks (3.5 THz) is evidenced by a strong (~1{\deg}) ultrafast Faraday rotation (~ 20 ps). In accordance with reference measurements and simulations, we estimated the strength of the induced magnetic field to be on the order of 0.7 T under a moderate pump fluence of about 440 nJ cm-2