1,414 research outputs found
Local Density of States and Order Parameter Configurations in Layered Ferromagnet-Superconductor Structures
We analyze the local density of states (LDOS) of heterostructures consisting
of alternating ferromagnet, , and superconductor, , layers. We consider
structures of the and type, with thin nanometer scale and
layers, within the ballistic regime. The spin-splitting effects of the
ferromagnet and the mutual coupling between the regions, yield several
nontrivial stable and metastable pair amplitude configurations, and we find
that the details of the spatial behavior of the pair amplitude govern the
calculated electronic spectra. These are reflected in discernible signatures of
the LDOS. The roles that the magnetic exchange energy, interface scattering
strength, and the Fermi wavevector mismatch each have on the LDOS for the
different allowed junction configurations, are systematically investigated.Comment: 20 pages, 10 figures. Figures are screen captures, high resolution
figures are available from either autho
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
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