51 research outputs found
Tuning the proximity effect in a superconductor-graphene-superconductor junction
We have tuned in situ the proximity effect in a single graphene layer coupled
to two Pt/Ta superconducting electrodes. An annealing current through the
device changed the transmission coefficient of the electrode/graphene
interface, increasing the probability of multiple Andreev reflections. Repeated
annealing steps improved the contact sufficiently for a Josephson current to be
induced in graphene.Comment: Accepted for publication in Phys. Rev.
Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3
A scheme is proposed to electrically measure the spin-momentum coupling in
the topological insulator surface state by injection of spin polarized
electrons from silicon. As a first approach, devices were fabricated consisting
of thin (<100nm) exfoliated crystals of Bi2Se3 on n-type silicon with
independent electrical contacts to silicon and Bi2Se3. Analysis of the
temperature dependence of thermionic emission in reverse bias indicates a
barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky
barrier opens the possibility of novel device designs based on sub-band gap
internal photoemission from Bi2Se3 into Si
PRE-NEOGENE DEFORMATION OF THE EASTERN CORDILLERA, AS EVIDENCED BY FORELAND STRATA
Cuatro pulsos de deformación, previo al evento Andino post-Mioceno Medio, se han definido para la Cordillera Oriental a partir de la integración de modelos estratigráficos, de procedencia, estructurales y geodinámicos. Los primeros dos pulsos, de edad Maastrichtiano Tardío y Paleoceno Tardío, fueron definidos por el cambio de patrón de acumulación y procedencia de los sedimentos en la cuenca de antepaís. El tercer pulso de edad Eoceno Temprano-Medio tiene como zona de deformación el flanco occidental de la Cordillera Oriental y el Valle del Magdalena, generando poco espacio de acomodación hacia el este donde se acumularon las formaciones Mirador-Picacho. El cuarto pulso de edad Eoceno tardío-Mioceno Medio se documenta en la zona norte del piedemonte por estratos de crecimientos, en la zona central por el abrupto cambio de espesor de los estratos, y por el inicio de la acumulación en la zona sur de los Llanos. El modelamiento geodinámico permitió establecer tanto la posición de las cargas como su magnitud con respecto al evento de deformación Andino post-Mioceno Medio. Estos cuatro pulsos pre-Mioceno Medio deben considerarse en futuros programas de exploración minera y de hidrocarburos.
Palabras clave: cuenca antepaís, Llanos, Cordillera Oriental, historia de levantamiento
Strata architecture, provenance, structural and Geodynamic analyses constrain the identification of 4 pulses of deformation,prior to the post-middle Miocene Andean pulse. Change of strata pattern of deposition and provenance in the foreland basin document the first two pulses during the late Maastrichtian-Paleocene time. In the Magdalena Valley and western flank of the Eastern Cordillera concentrated deformation of the third pulse, whereas amalgamated fluvial Mirador- Picacho sandstones accumulated in areas with low-accommodation space patterns. Late Eocene-Middle Miocene strata along the Llanos foothills and Llanos basins record, from north to south, growth strata patterns, abrupt lateral changes of thickness, and diachronous onset of deposition of synorogenic strata. Location of tectonic loads for each pulse was determined based on geodynamic modeling; this approach also allows us to quantify the amount of loading with respect to Andean tectonic loading. These four events of deformation should be considered in future hydrocarbon and mining exploration programs.
Keywords: foreland, Llanos, Eastern Cordillera, uplift histor
PRE-NEOGENE DEFORMATION OF THE EASTERN CORDILLERA, AS EVIDENCED BY FORELAND STRATA
Cuatro pulsos de deformación, previo al evento Andino post-Mioceno Medio, se han definido para la Cordillera Oriental a partir de la integración de modelos estratigráficos, de procedencia, estructurales y geodinámicos. Los primeros dos pulsos, de edad Maastrichtiano Tardío y Paleoceno Tardío, fueron definidos por el cambio de patrón de acumulación y procedencia de los sedimentos en la cuenca de antepaís. El tercer pulso de edad Eoceno Temprano-Medio tiene como zona de deformación el flanco occidental de la Cordillera Oriental y el Valle del Magdalena, generando poco espacio de acomodación hacia el este donde se acumularon las formaciones Mirador-Picacho. El cuarto pulso de edad Eoceno tardío-Mioceno Medio se documenta en la zona norte del piedemonte por estratos de crecimientos, en la zona central por el abrupto cambio de espesor de los estratos, y por el inicio de la acumulación en la zona sur de los Llanos. El modelamiento geodinámico permitió establecer tanto la posición de las cargas como su magnitud con respecto al evento de deformación Andino post-Mioceno Medio. Estos cuatro pulsos pre-Mioceno Medio deben considerarse en futuros programas de exploración minera y de hidrocarburos.
Palabras clave: cuenca antepaís, Llanos, Cordillera Oriental, historia de levantamiento
Strata architecture, provenance, structural and Geodynamic analyses constrain the identification of 4 pulses of deformation,prior to the post-middle Miocene Andean pulse. Change of strata pattern of deposition and provenance in the foreland basin document the first two pulses during the late Maastrichtian-Paleocene time. In the Magdalena Valley and western flank of the Eastern Cordillera concentrated deformation of the third pulse, whereas amalgamated fluvial Mirador- Picacho sandstones accumulated in areas with low-accommodation space patterns. Late Eocene-Middle Miocene strata along the Llanos foothills and Llanos basins record, from north to south, growth strata patterns, abrupt lateral changes of thickness, and diachronous onset of deposition of synorogenic strata. Location of tectonic loads for each pulse was determined based on geodynamic modeling; this approach also allows us to quantify the amount of loading with respect to Andean tectonic loading. These four events of deformation should be considered in future hydrocarbon and mining exploration programs.
Keywords: foreland, Llanos, Eastern Cordillera, uplift histor
Phonon assisted dynamical Coulomb blockade in a thin suspended graphite sheet
The differential conductance in a suspended few layered graphene sample is
fou nd to exhibit a series of quasi-periodic sharp dips as a function of bias
at l ow temperature. We show that they can be understood within a simple model
of dyn amical Coulomb blockade where energy exchanges take place between the
charge carriers transmitted trough the sample and a dissipative electromagnetic
envir onment with a resonant phonon mode strongly coupled to the electrons
Transport and elastic scattering times as probes of the nature of impurity scattering in single and bilayer graphene
Both transport and elastic scattering times are
experimentally determined from the carrier density dependence of the
magnetoconductance of monolayer and bilayer graphene. Both times and their
dependences in carrier density are found to be very different in the monolayer
and the bilayer. However their ratio is found to be of the
order of in both systems and independent of the carrier density. These
measurements give insight on the nature (neutral or charged) and spatial extent
of the scattering centers. Comparison with theoretical predictions yields that
the main scattering mechanism in our graphene samples could be due to strong
scatterers of short range, inducing resonant scattering, a likely candidate
being vacancies
Relativistic graphene ratchet on semidisk Galton board
Using extensive Monte Carlo simulations we study numerically and analytically
a photogalvanic effect, or ratchet, of directed electron transport induced by a
microwave radiation on a semidisk Galton board of antidots in graphene. A
comparison between usual two-dimensional electron gas (2DEG) and electrons in
graphene shows that ratchet currents are comparable at very low temperatures.
However, a large mean free path in graphene should allow to have a strong
ratchet transport at room temperatures. Also in graphene the ratchet transport
emerges even for unpolarized radiation. These properties open promising
possibilities for room temperature graphene based sensitive photogalvanic
detectors of microwave and terahertz radiation.Comment: 4 pages, 4 figures. Research done at Quantware
http://www.quantware.ups-tlse.fr/. More detailed analysis is give
Pinning and switching of magnetic moments in bilayer graphene
We examine the magnetic properties of the localized states induced by lattice
vacancies in bilayer graphene with an unrestricted Hartree-Fock calculation. We
show that with realistic values of the parameters and for experimentally
accessible gate voltages we can have a magnetic switching between an
unpolarized and a fully polarized system.Comment: 9 pages, 4 figure
Transport Through Andreev Bound States in a Graphene Quantum Dot
Andreev reflection-where an electron in a normal metal backscatters off a
superconductor into a hole-forms the basis of low energy transport through
superconducting junctions. Andreev reflection in confined regions gives rise to
discrete Andreev bound states (ABS), which can carry a supercurrent and have
recently been proposed as the basis of qubits [1-3]. Although signatures of
Andreev reflection and bound states in conductance have been widely reported
[4], it has been difficult to directly probe individual ABS. Here, we report
transport measurements of sharp, gate-tunable ABS formed in a
superconductor-quantum dot (QD)-normal system, which incorporates graphene. The
QD exists in the graphene under the superconducting contact, due to a
work-function mismatch [5, 6]. The ABS form when the discrete QD levels are
proximity coupled to the superconducting contact. Due to the low density of
states of graphene and the sensitivity of the QD levels to an applied gate
voltage, the ABS spectra are narrow, can be tuned to zero energy via gate
voltage, and show a striking pattern in transport measurements.Comment: 25 Pages, included SO
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