49,789 research outputs found
Conductance oscillations in mesoscopic rings: microscopic versus macroscopic picture
The phase of Aharonov-Bohm oscillations in mesoscopic metal rings in the
presence of a magnetic field can be modulated by application of a DC-bias
current I_DC. We address the question of how a variation of I_DC and hence of
the microscopic phases of the electronic wave functions results in the
macroscopic phase of the conductance oscillations. Whereas the first one can be
varied continuously the latter has to be quantized for a ring in two-wire
configuration by virtue of the Onsager symmetry relations. We observe a
correlation between a phase flip by +/- pi and the amplitude of the
oscillations.Comment: 4 pages, 4 figure
Vortices, zero modes and fractionalization in bilayer-graphene exciton condensate
A real-space formulation is given for the recently discussed exciton
condensate in a symmetrically biased graphene bilayer. We show that in the
continuum limit an oddly-quantized vortex in this condensate binds exactly one
zero mode per valley index of the bilayer. In the full lattice model the zero
modes are split slightly due to intervalley mixing. We support these results by
an exact numerical diagonalization of the lattice Hamiltonian. We also discuss
the effect of the zero modes on the charge content of these vortices and deduce
some of their interesting properties.Comment: (v2) A typo in Fig. 1 and a slight error in Eq. (4) corrected; all
the main results and conclusions remain unchange
Evidence for crossed Andreev reflection in superconductor-ferromagnet hybrid structures
We have measured the non-local resistance of aluminum-iron spin-valve
structures fabricated by e-beam lithography and shadow evaporation. The sample
geometry consists of an aluminum bar with two or more ferromagnetic wires
forming point contacts to the aluminum at varying distances from each other. In
the normal state of aluminum, we observe a spin-valve signal which allows us to
control the relative orientation of the magnetizations of the ferromagnetic
contacts. In the superconducting state, at low temperatures and excitation
voltages well below the gap, we observe a spin-dependent non-local resistance
which decays on a smaller length scale than the normal-state spin-valve signal.
The sign, magnitude and decay length of this signal is consistent with
predictions made for crossed Andreev reflection (CAR).Comment: RevTeX, 4 page
Dimensionality effects on non-equilibrium electronic transport in Cu nanobridges
We report on non-equilibrium electronic transport through normal-metal (Cu)
nanobridges coupled to large reservoirs at low temperatures. We observe a
logarithmic temperature dependence of the zero-bias conductance, as well as a
universal scaling behavior of the differential conductance. Our results are
explained by electron-electron interactions in diffusive metals in the
zero-dimensional limit.Comment: RevTex, 4 page
First record of an Odontaspidid shark in Ascension Island waters
The occurrence of the poorly understood shark species Odontapsis ferox is reported at an oceanic seamount in the central south Atlantic, within the Exclusive Economic Zone of Ascension Island. The presence of the species at this location is confirmed by the discovery of a tooth embedded in scientific equipment, and footage of at least one animal on autonomous underwater video. The new record of this shark species at this location demonstrates the knowledge gaps which still exist at many remote, oceanic structures and their candidacy for status as important conservation areas.info:eu-repo/semantics/publishedVersio
Feynman versus Bakamjian-Thomas in Light Front Dynamics
We compare the Bakamjian-Thomas (BT) formulation of relativistic few-body
systems with light front field theories that maintain closer contact with
Feynman diagrams. We find that Feynman diagrams distinguish Melosh rotations
and other kinematical quantities belonging to various composite subsystem
frames that correspond to different loop integrals. The BT formalism knows only
the rest frame of the whole composite system, where everything is evaluated.Comment: 5 page
Non-monotonic thermal Casimir force from geometry-temperature interplay
The geometry dependence of Casimir forces is significantly more pronounced in
the presence of thermal fluctuations due to a generic geometry-temperature
interplay. We show that the thermal force for standard sphere-plate or
cylinder-plate geometries develops a non-monotonic behavior already in the
simple case of a fluctuating Dirichlet scalar. In particular, the attractive
thermal force can increase for increasing distances below a critical
temperature. This anomalous behavior is triggered by a reweighting of relevant
fluctuations on the scale of the thermal wavelength. The essence of the
phenomenon becomes transparent within the worldline picture of the Casimir
effect.Comment: 4 pages, 4 figure
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