89 research outputs found
Effect of edge transmission and elastic scattering on the resistance of magnetic barriers
Strong magnetic barriers are defined in two-dimensional electron gases by
magnetizing dysprosium ferromagnetic platelets on top of a Ga[Al]As
heterostructure. A small resistance across the barrier is observed even deep
inside the closed regime. We have used semiclassical simulations to explain
this behavior quantitatively in terms of a combined effect of elastic electron
scattering inside the barrier region and E x B drift at the intersection of the
magnetic barrier with the edge of the Hall bar.Comment: 7 pages 4 figure
Absorption of Ultrashort Laser Pulses in Strongly Overdense Targets
We report on the first absorption experiments of sub-10 fs high-contrast
Ti:Sa laser pulses incident on solid targets. The very good contrast of the
laser pulse assures the formation of a very small pre-plasma and the pulse
interacts with the matter close to solid density. Experimental results indicate
that p-polarized laser pulses are absorbed up to 80 percent at 80 degrees
incidence angle. The simulation results of PSC PIC code clearly confirm the
observations and show that the collisionless absorption works efficiently in
steep density profiles
Relativistic electron acceleration by surface plasma waves excited with high intensity laser pulses
The process of high energy electron acceleration along the surface of grating targets (GTs) that were irradiated by a relativistic, high-contrast laser pulse at an intensity was studied. Our experimental results demonstrate that for a GT with a periodicity twice the laser wavelength, the surface electron flux is more intense for a laser incidence angle that is larger compared to the resonance angle predicted by the linear model. An electron beam with a peak charge of , for electrons with energies , was measured. Numerical simulations carried out with parameters similar to the experimental conditions also show an enhanced electron flux at higher incidence angles depending on the preplasma scale length. A theoretical model that includes ponderomotive effects with more realistic initial preplasma conditions suggests that the laser-driven intensity and preformed plasma scale length are important for the acceleration process. The predictions closely match the experimental and computational results
Sensing domain wall pinning in the longitudinal magnetoresistance of a two-dimensional electron gas
We investigate the sensing of domain wall pinning in thin Co wires positioned on top of a two-dimensional electron gas (2DEG) heterostructure by measuring the longitudinal resistance of the 2DEG as the magnetic field is swept, in an analogy to the Barkhausen effect. For comparison, we also measure the magnetoresistance of the ferromagnetic film in the same device in a subsequent sweep. Compared to the Hall measurements, the longitudinal measurement has the advantage of sensing magnetic activity over longer lengths, while compared to the measurement of the magnetoresistance in the ferromagnetic wire, it offers complementary information related to the pinning and unpinning of the domain wall, due to its sensitivity only to the out-of-plane magnetic field component.Fil: Kazazis, D.. No especifĂca;Fil: SchĂĽler, B.. Heinrich Heine University; AlemaniaFil: Granada, Mara. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Patagonia Norte; ArgentinaFil: Gennser, U.. No especifĂca;Fil: Faini, G.. No especifĂca;Fil: Cerchez, M.. Heinrich Heine University; AlemaniaFil: Heinzel, T.. Heinrich Heine University; Alemani
Harmonic Generation from Relativistic Plasma Surfaces in Ultra-Steep Plasma Density Gradients
Harmonic generation in the limit of ultra-steep density gradients is studied
experimentally. Observations demonstrate that while the efficient generation of
high order harmonics from relativistic surfaces requires steep plasma density
scale-lengths () the absolute efficiency of the harmonics
declines for the steepest plasma density scale-length , thus
demonstrating that near-steplike density gradients can be achieved for
interactions using high-contrast high-intensity laser pulses. Absolute photon
yields are obtained using a calibrated detection system. The efficiency of
harmonics reflected from the laser driven plasma surface via the Relativistic
Oscillating Mirror (ROM) was estimated to be in the range of 10^{-4} - 10^{-6}
of the laser pulse energy for photon energies ranging from 20-40 eV, with the
best results being obtained for an intermediate density scale-length
Extreme ultraviolet emission from dense plasmas generated with sub-10-fs laser pulses
The extreme ultraviolet (XUV) emission from dense plasmas generated with
sub-10-fs laser pulses with varying peak intensities up to 3*10^16 W/cm^2 is
investigated for different target materials. K shell spectra are obtained from
low Z targets (carbon and boron nitride). In the spectra a series limit for the
hydrogen and helium like resonance lines is observed indicating that the plasma
is at high density and pressure ionization has removed the higher levels. In
addition, L shell spectra from titanium targets were obtained. Basic features
of the K and L shell spectra are reproduced with computer simulations. The
calculations include hydrodynamic simulation of the plasma expansion and
collisional radiative calculations of the XUV emission.Comment: 22 pages, 11 figures. The following article has been submitted to
Physics of Plasmas. After it is published, it will be found at
http://pop.aip.org
Magnetic barrier induced conductance fluctuations in quantum wires
Quasi-ballistic semiconductor quantum wires are exposed to localized
perpendicular magnetic fields, also known as magnetic barriers. Pronounced,
reproducible conductance fluctuations as a function of the magnetic barrier
amplitude are observed. The fluctuations are strongly temperature dependent and
remain visible up to temperatures of about 10 K. Simulations based on recursive
Green functions suggest that the conductance fluctuations originate from
parametric interferences of the electronic wave functions which experience
scattering between the magnetic barrier and the electrostatic potential
landscape.Comment: 4 pages, 4 figure
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