10,292 research outputs found
Quantum states in a magnetic anti-dot
We study a new system in which electrons in two dimensions are confined by a
non homogeneous magnetic field. The system consists of a heterostructure with
on top of it a superconducting disk. We show that in this system electrons can
be confined into a dot region. This magnetic anti-dot has the interesting
property that the filling of the dot is a discrete function of the magnetic
field. The circulating electron current inside and outside the anti-dot can be
in opposite direction for certain bound states. And those states exhibit a
diamagnetic to paramagnetic transition with increasing magnetic field. The
absorption spectrum consists of many peaks, some of which violate Kohn's
theorem, and which is due to the coupling of the center of mass motion with the
other degrees of freedom.Comment: 6 pages, 12 ps figure
Few-electron eigenstates of concentric double quantum rings
Few-electron eigenstates confined in coupled concentric double quantum rings
are studied by the exact diagonalization technique. We show that the magnetic
field suppresses the tunnel coupling between the rings localizing the
single-electron states in the internal ring, and the few-electron states in the
external ring. The magnetic fields inducing the ground-state angular momentum
transitions are determined by the distribution of the electron charge between
the rings. The charge redistribution is translated into modifications of the
fractional Aharonov-Bohm period. We demonstrate that the electron distribution
can be deduced from the cusp pattern of the chemical potentials governing the
single-electron charging properties of the system. The evolution of the
electron-electron correlations to the high field limit of a classical Wigner
molecule is discussed.Comment: to appear in Physical Review
Tuning the polarized quantum phonon transmission in graphene nanoribbons
We propose systems that allow a tuning of the phonon transmission function
T() in graphene nanoribbons by using C isotope barriers, antidot
structures, and distinct boundary conditions. Phonon modes are obtained by an
interatomic fifth-nearest neighbor force-constant model (5NNFCM) and
T() is calculated using the non-equilibrium Green's function formalism.
We show that by imposing partial fixed boundary conditions it is possible to
restrict contributions of the in-plane phonon modes to T() at low
energy. On the contrary, the transmission functions of out-of-plane phonon
modes can be diminished by proper antidot or isotope arrangements. In
particular, we show that a periodic array of them leads to sharp dips in the
transmission function at certain frequencies which can be
pre-defined as desired by controlling their relative distance and size. With
this, we demonstrated that by adequate engineering it is possible to govern the
magnitude of the ballistic transmission functions T in graphene
nanoribbons. We discuss the implications of these results in the design of
controlled thermal transport at the nanoscale as well as in the enhancement of
thermo-electric features of graphene-based materials
Mixing the stimulus list in bilingual lexical decision turns cognate facilitation effects into mirrored inhibition effects
To test the BIA+ and Multilink models’ accounts of how bilinguals process words with different degrees of cross-linguistic orthographic and semantic overlap, we conducted two experiments manipulating stimulus list composition. Dutch-English late bilinguals performed two English lexical decision tasks including the same set of cognates, interlingual homographs, English control words, and pseudowords. In one task, half of the pseudowords were replaced with Dutch words, requiring a ‘no’ response. This change from pure to mixed language list context was found to turn cognate facilitation effects into inhibition. Relative to control words, larger effects were found for cognate pairs with an increasing cross-linguistic form overlap. Identical cognates produced considerably larger effects than non-identical cognates, supporting their special status in the bilingual lexicon. Response patterns for different item types are accounted for in terms of the items’ lexical representation and their binding to ‘yes’ and ‘no’ responses in pure vs mixed lexical decision
Veselago lensing in graphene with a p-n junction: classical versus quantum effects
The feasibility of Veselago lensing in graphene with a p-n junction is
investigated numerically for realistic injection leads. Two different set-ups
with two narrow leads are considered with absorbing or reflecting side edges.
This allows us to separately determine the influence of scattering on electron
focusing for the edges and the p-n interface. Both semiclassical and
tight-binding simulations show a distinctive peak in the transmission
probability that is attributed to the Veselago lensing effect. We investigate
the robustness of this peak on the width of the injector, the position of the
p-n interface and different gate potential profiles. Furthermore, the influence
of scattering by both short- and long-range impurities is considered.Comment: 10 pages, 7 figure
Helical liquid of snake states
We derive an exact solution to the problem of spin snake states induced in a
nonhomogeneous magnetic field by a combined action of the Rashba spin-orbit and
Zeeman fields. In an antisymmetric magnetic field the spin snake states are
nonlocal composite particles, originating from spatially separated entangled
spins. Adding an external homogeneous magnetic field breaks the spin-parity
symmetry gapping out the spectral branches, which results in a regular beating
pattern of the spin current. These new phenomena in a helical liquid of snake
states are proposed for an experimental realization.Comment: 5 pages, 3 figure
Strain controlled valley filtering in multi-terminal graphene structures
Valley-polarized currents can be generated by local straining of
multi-terminal graphene devices. The pseudo-magnetic field created by the
deformation allows electrons from only one valley to transmit and a current of
electrons from a single valley is generated at the opposite side of the locally
strained region. We show that valley filtering is most effective with bumps of
a certain height and width. Despite the fact that the highest contribution to
the polarized current comes from electrons from the lowest sub-band,
contributions of other sub-bands are not negligible and can significantly
enhance the output current.Comment: 4 pages, 4 figure
Partially unzipped carbon nanotubes as magnetic field sensors
The conductance, , through graphene nanoribbons (GNR) connected to a
partially unzipped carbon nanotube (CNT) is studied in the presence of an
external magnetic field applied parallel to the long axis of the tube by means
of non-equilibrium Green's function technique. We consider (z)igzag and
(a)rmchair CNTs that are partially unzipped to form aGNR/zCNT/aGNR or
zGNR/aCNT/zGNR junctions. We find that the inclusion of a longitudinal magnetic
field affects the electronic states only in the CNT region, leading to the
suppression of the conductance at low energies. Unlike previous studies, for
the zGNR/aCNT/zGNR junction in zero field, we find a sharp dip in the
conductance as the energy approaches the Dirac point and we attribute this
non-trivial behavior to the peculiar band dispersion of the constituent
subsystems. We demonstrate that both types of junctions can be used as magnetic
field sensors.Comment: final version to appear in Applied Physics Letter
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