3,351 research outputs found
Graphene-based extremely wide-angle tunable metamaterial absorber
We investigate the absorption properties of graphene-based anisotropic
metamaterial structures where the metamaterial layer possesses an
electromagnetic response corresponding to a near-zero permittivity. We find
that through analytical and numerical studies, near perfect absorption arises
over an unusually broad range of beam incidence angles. Due to the presence of
graphene, the absorption is tunable via a gate voltage, providing dynamic
control of the energy transmission. We show that this strongly enhanced
absorption arises due to a coupling between light and a fast wave-mode
propagating along the graphene/metamaterial hybrid.Comment: 9 pages, 6 figure
Superconducting Spintronics with Magnetic Domain Walls
The recent experimental demonstration of spin-polarized supercurrents offer a
venue for establishment of a superconducting analogue to conventional
spintronics. Whereas domain wall motion in purely magnetic structures is a
well-studied topic, it is not clear how domain wall dynamics may influence
superconductivity and if some functional property can be harnessed from such a
scenario. Here, we demonstrate that domain wall motion in superconducting
systems offers a unique way of controlling the quantum state of the
superconductor. Considering both the diffusive and ballistic limits, we show
that moving the domain wall to different locations in a Josephson junction will
change the quantum ground state from being in a 0 state to a state.
Remarkably, we also show that domain wall motion can be used to turn on and off
superconductivity: the position of the domain wall determines the critical
temperature and thus if the system is in a resistive state or not,
causing even a quantum phase transition between the dissipationless and normal
state at . In this way, one achieves dynamical control over the
superconducting state within a single sample by utilizing magnetic domain wall
motion
Polarization squeezing by optical Faraday rotation
We show that it is possible to generate continuous-wave fields and pulses of
polarization squeezed light by sending classical, linearly polarized laser
light twice through an atomic sample which causes an optical Faraday rotation
of the field polarization. We characterize the performance of the process, and
we show that an appreciable degree of squeezing can be obtained under realistic
physical assumptions.Comment: 4 pages, 4 figure
Singlet-Triplet Superconducting Quantum Magnetometer
Motivated by the recent experimental realization of a quantum interference
transistor based on the superconducting proximity effect, we here demonstrate
that the inclusion of a textured ferromagnet both strongly enhances the flux
sensitivity of such a device and additionally allows for singlet-triplet
switching by tuning a bias voltage. This functionality makes explicit use of
the induced spin-triplet correlations due to the magnetic texture. Whereas the
existence of such triplet correlations is well-known, our finding demonstrates
how spin-triplet superconductivity may be utilized for concrete technology,
namely to improve the functionality of ultra-sensitive magnetometers.Comment: 5 pages, 3 figures. To Appear in Physical Review
Lead markets for fuel cells in stationary applications
In the paper it is analysed which countries are likely to become the lead
markets for fuel cells in stationary applications. The study is part of a
larger research project “Policy Frameworks for the Development of
International Markets for Innovations of a Sustainable Economy - from Pilot
Markets to Lead Markets (LEAD)”. In the course of this project more than 20
environmental technologies were examined regarding the regional differences of
their market introduction and penetration. The project aims to explain why
some countries are earlier in the introduction of environmental innovations
and why the market penetration is more encompassing than in others. If the
technologies of the pioneering countries diffuse to other countries without
great modification, they can be analysed as lead markets for environmental
innovations. Fuel cells for electricity generation in stationary are an
emerging technology that is still in the stage of development and
demonstration. There are several competing innovation designs on the market,
and it is still open which technology is likely to be successful. The
different technologies are described and compared among each other, as well as
against conventional technologies for power generation. Three countries can be
identified as frontrunners in the development of fuel cells, namely the United
States, Japan and Germany. These countries are analysed regarding the R&D;
policies, the conditions for combined heat and power generation (CHP), the
structure of energy prices, and regarding environmental policies that aim at
internalising the environmental costs of energy production. The paper
evaluates the different activities to stimulate the development and market
introduction of fuel cells from a comparative perspective in order to assess
respective lead market potential
Dynamical effects of exchange symmetry breaking in mixtures of interacting bosons
In a double-well potential, a Bose-Einstein condensate exhibits Josephson
oscillations or self-trapping, depending on its initial preparation and on the
ratio of inter-particle interaction to inter-well tunneling. Here, we elucidate
the role of the exchange symmetry for the dynamics with a mixture of two
distinguishable species with identical physical properties, i.e. which are
governed by an isospecific interaction and external potential. In the
mean-field limit, the spatial population imbalance of the mixture can be
described by the dynamics of a single species in an effective potential with
modified properties or, equivalently, with an effective total particle number.
The oscillation behavior can be tuned by populating the second species while
maintaining the spatial population imbalance and all other parameters constant.
In the corresponding many-body approach, the single-species description
approximates the full counting statistics well also outside the realm of
spin-coherent states. The method is extended to general Bose-Hubbard systems
and to their classical mean-field limits, which suggests an effective
single-species description of multicomponent Bose gases with weakly
an-isospecific interactions.Comment: amended and expanded, accepted for Phys. Rev. A, 14 pages, 7 figure
- …