81 research outputs found
Thermal transport driven by charge imbalance in graphene in magnetic field, close to the charge neutrality point at low temperature: Non local resistance
Graphene grown epitaxially on SiC, close to the charge neutrality point
(CNP), in an orthogonal magnetic field shows an ambipolar behavior of the
transverse resistance accompanied by a puzzling longitudinal magnetoresistance.
When injecting a transverse current at one end of the Hall bar, a sizeable non
local transverse magnetoresistance is measured at low temperature. While Zeeman
spin effect seems not to be able to justify these phenomena, some dissipation
involving edge states at the boundaries could explain the order of magnitude of
the non local transverse magnetoresistance, but not the asymmetry when the
orientation of the orthogonal magnetic field is reversed. As a possible
contribution to the explanation of the measured non local magnetoresistance
which is odd in the magnetic field, we derive a hydrodynamic approach to
transport in this system, which involves particle and hole Dirac carriers, in
the form of charge and energy currents. We find that thermal diffusion can take
place on a large distance scale, thanks to long recombination times, provided a
non insulating bulk of the Hall bar is assumed, as recent models seem to
suggest in order to explain the appearance of the longitudinal resistance. In
presence of the local source, some leakage of carriers from the edges generates
an imbalance of carriers of opposite sign, which are separated in space by the
magnetic field and diffuse along the Hall bar generating a non local transverse
voltage.Comment: 25 pages, 12 figure
Rashba-control for the spin excitation of a fully spin polarized vertical quantum dot
Far infrared radiation absorption of a quantum dot with few electrons in an
orthogonal magnetic field could monitor the crossover to the fully spin
polarized state. A Rashba spin-orbit coupling can tune the energy and the spin
density of the first excited state which has a spin texture carrying one extra
unit of angular momentum. The spin orbit coupling can squeeze a flipped spin
density at the center of the dot and can increase the gap in the spectrum.Comment: 4 pages, 5 figure
Mesoscopic conductance fluctuations in YBaCuO grain boundary Junction at low temperature
The magneto-conductance in YBCO grain boundary Josephson junctions, displays
fluctuations at low temperatures of mesoscopic origin. The morphology of the
junction suggests that transport occurs in narrow channels across the grain
boundary line, with a large Thouless energy. Nevertheless the measured
fluctuation amplitude decreases quite slowly when increasing the voltage up to
values about twenty times the Thouless energy, of the order of the nominal
superconducting gap. Our findings show the coexistence of supercurrent and
quasiparticle current in the junction conduction even at high nonequilibrium
conditions. Model calculations confirm the reduced role of quasiparticle
relaxation at temperatures up to 3 Kelvin.Comment: 11 pages, 5 figures, accepted with minor changes in Phys.Rev.
Coherent quasiparticle transport in grain boundary junctions employing high-Tc superconductors
Magneto-fluctuations of the normal resistance RN have been reproducibly
observed in YBa2Cu3O7-d biepitaxial grain boundary junctions at low
temperatures. We attribute them to mesoscopic transport in narrow channels
across the grain boundary line, occurring in an unusual energy regime. The
Thouless energy appears to be the relevant energy scale. Possible implications
on the understanding of coherent transport of quasiparticles in HTS and of the
dissipation mechanisms are discussed.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Spin Exciton in quantum dot with spin orbit coupling in high magnetic field
Coulomb interactions of few () electrons confined in a disk shaped
quantum dot, with a large magnetic field applied in the z-direction
(orthogonal to the dot), produce a fully spin polarized ground state. We
numerically study the splitting of the levels corresponding to the multiplet of
total spin (each labeled by a different total angular momentum )
in presence of an electric field parallel to , coupled to by a
Rashba term. We find that the first excited state is a spin exciton with a
reversed spin at the origin. This is reminiscent of the Quantum Hall
Ferromagnet at filling one which has the skyrmion-like state as its first
excited state. The spin exciton level can be tuned with the electric field and
infrared radiation can provide energy and angular momentum to excite it.Comment: 9 pages, 9 figures. submitted to Phys.Rev.
Coherent quasiparticle transport in grain boundary junctions employing high-Tc superconductors
mesoscopic physics, nanodevices, high critical temperature superconductorsMagneto-fluctuations of the normal resistance RN have been reproducibly observed in YBa2Cu3O7-ä biepitaxial grain boundary junctions at low temperatures. We attribute them to mesoscopic transport in narrow channels across the grain boundary line, occurring in an unusual energy regime. The Thouless energy appears to be the relevant energy scale. Possible implications on the understanding of coherent transport of quasiparticles in HTS and of the dissipation mechanisms are discussed
What happens in Josephson junctions at high critical current densities
The impressive advances in material science and nanotechnology are more and more promoting the use of exotic barriers and/or superconductors, thus paving the way to new families of Josephson junctions. Semiconducting, ferromagnetic, topological insulator and graphene barriers are leading to unconventional and anomalous aspects of the Josephson coupling, which might be useful to respond to some issues on key problems of solid state physics. However, the complexity of the layout and of the competing physical processes occurring in the junctions is posing novel questions on the interpretation of their phenomenology. We classify some significant behaviors of hybrid and unconventional junctions in terms of their first imprinting, i.e., current-voltage curves, and propose a phenomenological approach to describe some features of junctions characterized by relatively high critical current densities Jc. Accurate arguments on the distribution of switching currents will provide quantitative criteria to understand physical processes occurring in high- Jc junctions. These notions are universal and apply to all kinds of junctions
- …