83 research outputs found
Quark--hadron duality in lepton scattering off nuclei
A phenomenological study of quark--hadron duality in electron and neutrino
scattering on nuclei is performed. We compute the structure functions and
in the resonance region within a framework that includes the
Dortmund-group model for the production of the {f}{i}rst four lowest-lying
baryonic resonances and a relativistic mean-field model for nuclei. We consider
four-momentum transfers between 0.2 and 2.5 GeV. The results indicate that
nuclear effects play a different role in the resonance and DIS region. We find
that global but not local duality works well. In the studied range of
four-momentum transfers, the integrated strength of the computed nuclear
structure functions in the resonance region, is considerably lower than the DIS
one.Comment: 18 pages, 11 figure
Cones, pringles, and grain boundary landscapes in graphene topology
A polycrystalline graphene consists of perfect domains tilted at angle
{\alpha} to each other and separated by the grain boundaries (GB). These nearly
one-dimensional regions consist in turn of elementary topological defects,
5-pentagons and 7-heptagons, often paired up into 5-7 dislocations. Energy
G({\alpha}) of GB computed for all range 0<={\alpha}<=Pi/3, shows a slightly
asymmetric behavior, reaching ~5 eV/nm in the middle, where the 5's and 7's
qualitatively reorganize in transition from nearly armchair to zigzag
interfaces. Analysis shows that 2-dimensional nature permits the off-plane
relaxation, unavailable in 3-dimensional materials, qualitatively reducing the
energy of defects on one hand while forming stable 3D-landsapes on the other.
Interestingly, while the GB display small off-plane elevation, the random
distributions of 5's and 7's create roughness which scales inversely with
defect concentration, h ~ n^(-1/2)Comment: 9 pages, 4 figure
Ballistic Josephson junctions in edge-contacted graphene
Hybrid graphene-superconductor devices have attracted much attention since
the early days of graphene research. So far, these studies have been limited to
the case of diffusive transport through graphene with poorly defined and modest
quality graphene-superconductor interfaces, usually combined with small
critical magnetic fields of the superconducting electrodes. Here we report
graphene based Josephson junctions with one-dimensional edge contacts of
Molybdenum Rhenium. The contacts exhibit a well defined, transparent interface
to the graphene, have a critical magnetic field of 8 Tesla at 4 Kelvin and the
graphene has a high quality due to its encapsulation in hexagonal boron
nitride. This allows us to study and exploit graphene Josephson junctions in a
new regime, characterized by ballistic transport. We find that the critical
current oscillates with the carrier density due to phase coherent interference
of the electrons and holes that carry the supercurrent caused by the formation
of a Fabry-P\'{e}rot cavity. Furthermore, relatively large supercurrents are
observed over unprecedented long distances of up to 1.5 m. Finally, in the
quantum Hall regime we observe broken symmetry states while the contacts remain
superconducting. These achievements open up new avenues to exploit the Dirac
nature of graphene in interaction with the superconducting state.Comment: Updated version after peer review. Includes supplementary material
and ancillary file with source code for tight binding simulation
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UNISOR on-Line Nuclear Orientation Facility (UNISOR/NOF)
The UNISOR on-line nuclear orientation facility (UNISOR/NOF) consists of a /sup 3/He--/sup 4/He dilution refrigerator on line to the isotope separator. Nuclei are implanted directly into a target foil which is soldered to the bottom accessed cold finger of the refrigerator. A 1.5 T superconducting magnet polarizes the ferromagnetic target foils and determines the axis of symmetry. Up to eight gamma detectors can be positioned around the refrigerator, each 9 cm from the target. A unique feature of this system is that the k = 4 term in the directional distribution function can be directly and unambiguously deduced so that a single solution for the mixing ratio can be found. The first on-line experiment at this facility reported here was a study of the decay of the /sup 191/Hg and /sup 193/Hg isotopes. 5 refs., 4 figs., 1 tab
Transverse Electronic Transport through DNA Nucleotides with Functionalized Graphene Electrodes
Graphene nanogaps and nanopores show potential for the purpose of electrical
DNA sequencing, in particular because single-base resolution appears to be
readily achievable. Here, we evaluated from first principles the advantages of
a nanogap setup with functionalized graphene edges. To this end, we employed
density functional theory and the non-equilibrium Green's function method to
investigate the transverse conductance properties of the four nucleotides
occurring in DNA when located between the opposing functionalized graphene
electrodes. In particular, we determined the electrical tunneling current
variation as a function of the applied bias and the associated differential
conductance at a voltage which appears suitable to distinguish between the four
nucleotides. Intriguingly, we observe for one of the nucleotides a negative
differential resistance effect.Comment: 19 pages, 7 figure
Lithography-free Fabrication of High Quality Substrate-supported and Freestanding Graphene devices
We present a lithography-free technique for fabrication of clean, high
quality graphene devices. This technique is based on evaporation through hard
Si shadow masks, and eliminates contaminants introduced by lithographical
processes. We demonstrate that devices fabricated by this technique have
significantly higher mobility values than those by standard electron beam
lithography. To obtain ultra-high mobility devices, we extend this technique to
fabricate suspended graphene samples with mobility as high as 120,000 cm^2/Vs
UNISOR on-line nuclear orientation facility (UNISOR/NOF)
The UNISOR on-line nuclear orientation facility (UNISOR/NOF) consists of a3He-4He dilution refrigerator on line to the isotope separator. Nuclei are implanted directly into a target foil which is soldered to the bottom accessed cold finger of the refrigerator. A 1.5 T superconducting magnet polarizes the ferromagnetic target foils and determines the axis of symmetry. Up to eight gamma detectors can be positioned around the refrigerator, each 9 cm from the target. A unique feature of this system is that the k=4 term in the directional distribution function can be directly and unambigously deduced so that a single solution for the mixing ratio can be found. The first on-line experiment at this facility reported here was a study of the decay of the191Hg and193Hg isotopes. © 1998 J.C. Baltzer A.G., Scientific Publishing Company
Quantum oscillations of the critical current and high-field superconducting proximity in ballistic graphene
Graphene-based Josephson junctions provide a novel platform for studying the
proximity effect due to graphene's unique electronic spectrum and the
possibility to tune junction properties by gate voltage. Here we describe
graphene junctions with a mean free path of several micrometres, low contact
resistance and large supercurrents. Such devices exhibit pronounced
Fabry-P\'erot oscillations not only in the normal-state resistance but also in
the critical current. The proximity effect is mostly suppressed in magnetic
fields below 10mT, showing the conventional Fraunhofer pattern. Unexpectedly,
some proximity survives even in fields higher than 1 T. Superconducting states
randomly appear and disappear as a function of field and carrier concentration,
and each of them exhibits a supercurrent carrying capacity close to the
universal quantum limit. We attribute the high-field Josephson effect to
mesoscopic Andreev states that persist near graphene edges. Our work reveals
new proximity regimes that can be controlled by quantum confinement and
cyclotron motion
Repeated growth and bubbling transfer of graphene with millimetre-size single-crystal grains using platinum
Large single-crystal graphene is highly desired and important for the applications of graphene in electronics, as grain boundaries between graphene grains markedly degrade its quality and properties. Here we report the growth of millimetre-sized hexagonal single-crystal graphene and graphene films joined from such grains on Pt by ambient-pressure chemical vapour deposition. We report a bubbling method to transfer these single graphene grains and graphene films to arbitrary substrate, which is nondestructive not only to graphene, but also to the Pt substrates. The Pt substrates can be repeatedly used for graphene growth. The graphene shows high crystal quality with the reported lowest wrinkle height of 0.8 nm and a carrier mobility of greater than 7,100 cm2 V−1 s−1 under ambient conditions. The repeatable growth of graphene with large single-crystal grains on Pt and its nondestructive transfer may enable various applications
Description of Even-Even Xe isotopes in the transitional region of IBM
Properties of Xe isotopes isotopes are studied in the U(5)O(6)
transitional region of Interacting Boson Model (IBM-1). The energy levels and
B(E2)transition rates are calculated via the affine SU(1,1)Lie Algebra. The
agreement with the most recent experimental is acceptable. The evaluated
Hamiltonian control parameters suggest a spherical to (/gamma)-soft shape
transition and propose the Xe(A=130)nucleus as the best candidate for the
E(5)symmetry.Comment: 15 pages,3 figures. I have received an email from the BJPH editor
(Prof.Luiz Nunes de Oliveira)which order me to resubmit the final version of
paper and note that, paper will appear in Volume 43 of the Brazilian Journal
of Physic
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