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Träfflista för sökning "WFRF:(Olbrich P) "

Sökning: WFRF:(Olbrich P)

  • Resultat 1-10 av 21
  • [1]23Nästa
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1.
  • de Graauw, Th., et al. (författare)
  • The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI)
  • 2010
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 518, s. L6-
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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3.
  • Karch, J., et al. (författare)
  • Terahertz Radiation Driven Chiral Edge Currents in Graphene
  • 2011
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 107:27
  • Tidskriftsartikel (refereegranskat)abstract
    • We observe photocurrents induced in single-layer graphene samples by illumination of the graphene edges with circularly polarized terahertz radiation at normal incidence. The photocurrent flows along the sample edges and forms a vortex. Its winding direction reverses by switching the light helicity from left to right handed. We demonstrate that the photocurrent stems from the sample edges, which reduce the spatial symmetry and result in an asymmetric scattering of carriers driven by the radiation electric field. The developed theory based on Boltzmann's kinetic equation is in a good agreement with the experiment. We show that the edge photocurrents can be applied for determination of the conductivity type and the momentum scattering time of the charge carriers in the graphene edge vicinity.
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6.
  • Drexler, C, et al. (författare)
  • Magnetic quantum ratchet effect in graphene
  • 2013
  • Ingår i: Nature Nanotechnology. - : Nature Publishing Group. - 1748-3387 .- 1748-3395. ; 8:2, s. 104-107
  • Tidskriftsartikel (refereegranskat)abstract
    • A periodically driven system with spatial asymmetry can exhibit a directed motion facilitated by thermal or quantum fluctuations(1). This so-called ratchet effect(2) has fascinating ramifications in engineering and natural sciences(3-18). Graphene(19) is nominally a symmetric system. Driven by a periodic electric field, no directed electric current should flow. However, if the graphene has lost its spatial symmetry due to its substrate or adatoms, an electronic ratchet motion can arise. We report an experimental demonstration of such an electronic ratchet in graphene layers, proving the underlying spatial asymmetry. The orbital asymmetry of the Dirac fermions is induced by an in-plane magnetic field, whereas the periodic driving comes from terahertz radiation. The resulting magnetic quantum ratchet transforms the a.c. power into a d.c. current, extracting work from the out-of-equilibrium electrons driven by undirected periodic forces. The observation of ratchet transport in this purest possible two-dimensional system indicates that the orbital effects may appear and be substantial in other two-dimensional crystals such as boron nitride, molybdenum dichalcogenides and related heterostructures. The measurable orbital effects in the presence of an in-plane magnetic field provide strong evidence for the existence of structure inversion asymmetry in graphene.
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7.
  • Drexler, C., et al. (författare)
  • Magnetic quantum ratchet effect in graphene
  • 2013
  • Ingår i: Nature Nanotechnology. - 1748-3387. ; 8:2, s. 104-107
  • Tidskriftsartikel (refereegranskat)abstract
    • A periodically driven system with spatial asymmetry can exhibit a directed motion facilitated by thermal or quantum fluctuations(1). This so-called ratchet effect(2) has fascinating ramifications in engineering and natural sciences(3-18). Graphene(19) is nominally a symmetric system. Driven by a periodic electric field, no directed electric current should flow. However, if the graphene has lost its spatial symmetry due to its substrate or adatoms, an electronic ratchet motion can arise. We report an experimental demonstration of such an electronic ratchet in graphene layers, proving the underlying spatial asymmetry. The orbital asymmetry of the Dirac fermions is induced by an in-plane magnetic field, whereas the periodic driving comes from terahertz radiation. The resulting magnetic quantum ratchet transforms the a.c. power into a d.c. current, extracting work from the out-of-equilibrium electrons driven by undirected periodic forces. The observation of ratchet transport in this purest possible two-dimensional system indicates that the orbital effects may appear and be substantial in other two-dimensional crystals such as boron nitride, molybdenum dichalcogenides and related heterostructures. The measurable orbital effects in the presence of an in-plane magnetic field provide strong evidence for the existence of structure inversion asymmetry in graphene.
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9.
  • Ganichev, S.D., et al. (författare)
  • Magnetic quantum ratchet effect in graphene
  • 2013
  • Ingår i: 38th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2013, Mainz, Germany, 1-6 September 2013. - 2162-2027.
  • Konferensbidrag (refereegranskat)abstract
    • We report on the observation of magnetic quantum ratchet (MQR) effect induced by electric field of terahertz radiation in single-layer graphene samples subjected to an inplane magnetic field. We show that the dc electric current stems from the orbital asymmetry of the Dirac fermions induced by an in-plane magnetic field, while the periodic driving comes from terahertz radiation. A microscopic theory of the observed effect is developed being in a good qualitative agreement with the experiment. The observation of the ratchet transport in the purest possible two-dimensional system indicates that the orbital effects may appear and be substantial in other 2D crystals, such as boron nitride, molybdenum dichalcogenides, and related heterostructures. The measurable orbital effects in the presence of an in-plane magnetic field give strong evidence for the existence of structure inversion asymmetry in graphene.
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10.
  • Drexler, C., et al. (författare)
  • Reststrahlen Band assisted photocurrents in graphene
  • 2013
  • Ingår i: 2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2013; Mainz; Germany; 1 September 2013 through 6 September 2013. - 2162-2035.
  • Konferensbidrag (refereegranskat)abstract
    • We report on the experimental and theoretical study of the Reststrahlen Band assisted photocurrents in epitaxial grown graphene on SiC. We show that excitation of graphene with infrared radiation results in a dc current. We demonstrate that photocurrent in response to linearly polarized radiation exhibit a resonance enhancement in the frequency range of the Reststrahlen Band of the SiC substrate. By contrast the photocurrent excited by circularly polarized radiation is suppressed in the same spectral range. The developed theory is in agreement with the data and reveals a strong influence of the Reststrahl Band on the high frequency transport in graphene.
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  • Resultat 1-10 av 21
  • [1]23Nästa

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