| 1. |
- Drexler, C, et al.
(author)
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Magnetic quantum ratchet effect in graphene
- 2013
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In: Nature Nanotechnology. - : Nature Publishing Group. - 1748-3387 .- 1748-3395. ; 8:2, s. 104-107
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Journal article (peer-reviewed)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.
(author)
-
Magnetic quantum ratchet effect in graphene
- 2013
-
In: Nature Nanotechnology. - 1748-3387 .- 1748-3395. ; 8:2, s. 104-107
-
Journal article (peer-reviewed)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. |
- Fadeel, B, et al.
(author)
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Broaden the discussion
- 2013
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In: Nature nanotechnology. - : Springer Science and Business Media LLC. - 1748-3395 .- 1748-3387. ; 8:2, s. 71-71
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Journal article (other academic/artistic)
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| 4. |
- Gustafsson, David, 1982, et al.
(author)
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Fully gapped superconductivity in a nanometresize YBa2Cu3O7-delta island enhanced by a magnetic field
- 2013
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In: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 8:1, s. 25-30
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Journal article (peer-reviewed)abstract
- The symmetry of Cooper pairs is central to constructing a superconducting state. The demonstration of a d(x2-y2)-wave order parameter with nodes represented a breakthrough for high critical temperature superconductors (HTSs)(1,2). However, despite this fundamental discovery, the origin of superconductivity remains elusive, raising the question of whether something is missing from the global picture. Deviations from d(x2-y2)-wave symmetry(3,4), such as an imaginary admixture d(x2-y2) + is (or id(xy)), predict a ground state with unconventional properties exhibiting a full superconducting gap and time reversal symmetry breaking(5). The existence of such a state, until now highly controversial(6-10), can be proved by highly sensitive measurements of the excitation spectrum. Here, we present a spectroscopic technique based on an HTS nanoscale device that allows an unprecedented energy resolution thanks to Coulomb blockade effects, a regime practically inaccessible in these materials previously. We find that the energy required to add an extra electron depends on the parity (odd/even) of the excess electrons on the island and increases with magnetic field. This is inconsistent with a pure d(x2-y2)-wave symmetry and demonstrates a complex order parameter component that needs to be incorporated into any theoretical model of HTS.
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| 5. |
- Hilty, Florentine M., et al.
(author)
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Iron from nanocompounds containing iron and zinc is highly bioavailable in rats without tissue accumulation
- 2010
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In: Nature Nanotechnology. - 1748-3387 .- 1748-3395. ; 5:5, s. 374-380
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Journal article (peer-reviewed)abstract
- Effective iron fortification of foods is difficult, because water-soluble compounds that are well absorbed, such as ferrous sulphate (FeSO(4)), often cause unacceptable changes in the colour or taste of foods. Poorly water-soluble compounds, on the other hand, cause fewer sensory changes, but are not well absorbed. Here, we show that poorly water-soluble nanosized Fe and Fe/Zn compounds (specific surface area similar to 190 m(2) g(-1)) made by scalable flame aerosol technology have in vivo iron bioavailability in rats comparable to FeSO(4) and cause less colour change in reactive food matrices than conventional iron fortificants. The addition of Zn to FePO(4) and Mg to Fe/Zn oxide increases Fe absorption from the compounds, and doping with Mg also improves their colour. After feeding rats with nanostructured iron-containing compounds, no stainable Fe was detected in their gut wall, gut-associated lymphatics or other tissues, suggesting no adverse effects. Nanosizing of poorly water-soluble Fe compounds sharply increases their absorption and nutritional value.
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| 6. |
- Jesorka, Aldo, 1967, et al.
(author)
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NANOFLUIDICS Neither shaken nor stirred
- 2012
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In: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 7:1, s. 6-7
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Journal article (peer-reviewed)
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| 7. |
- Kampfrath, T., et al.
(author)
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Terahertz spin current pulses controlled by magnetic heterostructures
- 2013
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In: Nature Nanotechnology. - 1748-3387 .- 1748-3395. ; 8:4, s. 256-260
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Journal article (peer-reviewed)abstract
- In spin-based electronics, information is encoded by the spin state of electron bunches(1-4). Processing this information requires the controlled transport of spin angular momentum through a solid(5,6), preferably at frequencies reaching the so far unexplored terahertz regime(7-9). Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins(10-12) from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter(13) based on the inverse spin Hall effect(14,15), which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states(16). Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters(7-9).
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| 8. |
- Kapaklis, Vassilios, et al.
(author)
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Thermal fluctuations in artificial spin ice
- 2014
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In: Nature Nanotechnology. - 1748-3387 .- 1748-3395. ; 9:7, s. 514-519
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Journal article (peer-reviewed)abstract
- Artificial spin ice systems have been proposed as a playground for the study of monopole-like magnetic excitations(1,2), similar to those observed in pyrochlore spin ice materials(3). Currents of magnetic monopole excitations have been observed's, demonstrating the possibility for the realization of magnetic-charge-based circuitry. Artificial spin ice systems that support thermal fluctuations can serve as an ideal setting for observing dynamical effects such as monopole propagation and as a potential medium for magnetricity investigations(1,2). Here, we report on the transition from a frozen to a dynamic state in artificial spin ice with a square lattice. Magnetic imaging is used to determine the magnetic state of the islands in thermal equilibrium. The temperature-induced onset of magnetic fluctuations and excitation populations are shown to depend on the lattice spacing and related interaction strength between islands. The excitations are described by Boltzmann distributions with their factors in the frozen state relating to the blocking temperatures of the array. Our results provide insight into the design of thermal artificial spin ice arrays where the magnetic charge density and response to external fields can be studied in thermal equilibrium.
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| 9. |
- Käll, Mikael, 1963
(author)
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Biosensors: One molecule at a time
- 2012
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In: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 7:6, s. 347-349
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Research review (peer-reviewed)
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| 10. |
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