| 1. |
- Drexler, C, et al.
(författare)
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Magnetic quantum ratchet effect in graphene
- 2013
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Ingår i: Nature Nanotechnology. - : Nature Publishing Group. - 1748-3387 .- 1748-3395. ; 8:2, s. 104-107
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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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| 2. |
- Drexler, C., et al.
(författare)
-
Magnetic quantum ratchet effect in graphene
- 2013
-
Ingår i: Nature Nanotechnology. - 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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| 3. |
- Ganichev, S.D., et al.
(författare)
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Magnetic quantum ratchet effect in graphene
- 2013
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Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. - 9781467347174
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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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| 4. |
- Drexler, C., et al.
(författare)
-
Terahertz radiation induced edge currents in graphene
- 2011
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Ingår i: RMMW-THz 2011 - 36th International Conference on Infrared, Millimeter, and Terahertz Waves. - 9781457705090
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Konferensbidrag (refereegranskat)abstract
- We report on the observation of the terahertz radiation induced edge photogalvanic effect. The directed net electric current is generated in single layer graphene by the irradiation of the samples' edges with linearly or circularly polarized terahertz laser radiation at normal incidence. We show that the directed net electric current stems from the sample edges, which reduce locally the symmetry and result in an asymmetric scattering of carriers driven by the radiation field.
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| 5. |
- Ganichev, S.D., et al.
(författare)
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Photon helicity driven currents in graphene
- 2010
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Ingår i: IRMMW-THz 2010 - 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Conference Guide. - 9781424466573
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We report on the observation of photon helicity driven currents in graphene. We demonstrate that by illuminating unbiased monolayer graphene samples with terahertz (THz) laser radiation at room temperature under oblique and normal incidence causes directed electric currents. This includes currents which are solely driven by the light's helicity.
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| 6. |
- Karch, J., et al.
(författare)
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Dynamic Hall Effect Driven by Circularly Polarized Light in a Graphene Layer
- 2010
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 105:22, s. 227402-
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Tidskriftsartikel (refereegranskat)abstract
- We report the observation of the circular ac Hall effect where the current is solely driven by the crossed ac electric and magnetic fields of circularly polarized radiation. Illuminating an unbiased monolayer sheet of graphene with circularly polarized terahertz radiation at room temperature generates-under oblique incidence-an electric current perpendicular to the plane of incidence, whose sign is reversed by switching the radiation helicity. Alike the classical dc Hall effect, the voltage is caused by crossed E and B fields which are, however rotating with the lights frequency.
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| 7. |
- Karch, J., et al.
(författare)
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Terahertz Radiation Driven Chiral Edge Currents in Graphene
- 2011
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Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 107:27
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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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| 8. |
- Olbrich, P., et al.
(författare)
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Terahertz radiation induced photocurrents in graphene subjected to an in-plane magnetic field
- 2012
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Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. - 9781467315975
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Konferensbidrag (refereegranskat)abstract
- We report on the observation of terahertz radiation induced photocurrents in single-layer graphene samples subjected to an in-plane magnetic field. The photosignal is observed for both, linearly and circularly polarized radiation. A remarkable effect is that the current inverts its sign not only by switching the magnetic field direction, but as well by changing the radiation helicity from left- to right-handedness. We demonstrate that the photocurrent stems from strong structure inversion asymmetry (SIA) of samples originating from the presence of substrate and/or adatoms on graphene. The analysis shows that the observed effect represents a new type of ratchet effects: magnetic field induced ratchets. A microscopic theory of the observed effect is developed being in a good qualitative agreement with the experiment. Furthermore, the experiments open a promising access to the investigation of SIA which is of particular interest for the understanding of graphene properties as well as applications.
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