1,721,146 research outputs found
Quantum tunnelling of electrons through a double barrier in a transverse magnetic field
No full textThe effect of a transverse magnetic field on the tunnelling probability of electrons in a double-barrier potential is investigated through a direct numerical solution of the one-dimensional effective-mass equation. The value of the transmission coefficient at resonance is found to be unaffected by the field: however, the peak in the I-V characteristic of the double barrier as a diode is markedly decreased when the magnetic field strength is increased, owing to the charge in the electron transverse momentum induced by the field
THEORY OF ELECTRON-ESCAPE FROM THE SURFACE OF LIQUID-HELIUM
No full textWe have studied the properties of an electron bubble close to the surface of liquid He-4, by using a Density Functional approach. We find that up to an electron-surface distance d(0) similar to 23 Angstrom the bubble is stable, while at smaller distances it becomes unstable and bursts. A potential energy barrier Phi/K-B similar to 38 degrees K for the thermal emission of electrons is obtained from our results, in agreement with experiments. Even when the electron-surface distance is larger than do, however, tunneling through the surface layer dominates the electron escape probability. Large deviations of the electron potential energy from its ideal value are found close to the surface. These deviations have a profound effect on the calculated decay rates of the tunneling curent, which are much smaller than those obtained previously and in semi-quantitative agreement with experiments
PROPERTIES OF AN ELECTRON BUBBLE APPROACHING THE SURFACE OF LIQUID-HELIUM
No full textWe have studied the properties of an electron bubble close to the surface of liquid He-4, by using a Density Functional approach. We find that up to an electron-surface distance d(0) similar to 23 Angstrom the bubble is stable, while at smaller distances it becomes unstable and bursts. A potential energy barrier Phi/K-B similar to 38 degrees K for the thermal emission of electrons is obtained from our results, in agreement with experiments. Even when the electron-surface distance is larger than do, however, tunneling through the surface layer dominates the electron escape probability. Large deviations of the electron potential energy from its ideal value are found close to the surface. These deviations have a profound effect on the calculated decay rates of the tunneling curent, which are much smaller than those obtained previously and in semi-quantitative agreement with experiments
Dipolar Bose gas in a highly anharmonic trap
No full textBy means of mean-field theory, we have studied the structure and excitation spectrum of a purely dipolar
Bose gas in a pancake shaped trap where the confinement in the x-y plane is provided by a highly anharmonic
potential, resulting in an almost uniform confinement in the plane. We show that the stable condensates are
characterized by marked radially structured density profiles. The stability diagram is calculated by independently
varying the strength of the interaction and the trap geometry. By computing the Bogoliubov excitation spectrum
near the instability line we show that soft “angular” rotons are responsible for the collapse of the system. The
free expansion of the cloud after the trap is released is also studied by means of time-dependent calculations,
showing that a prolate cigar-shaped condensate is dynamically stabilized during the expansion, which would
otherwise collapse. Dipolar condensates rotating with sufficiently high angular velocity show the formation of
multiply quantized giant vortices, while the condensates acquire a ring-shaped form
Prewetting transitions of Ar and Ne on alkali-metal surfaces
No full textWe have studied by means of density-functional calculations the wetting properties of Ar and Ne adsorbed on a plane whose adsorption properties simulate the Li and Na surfaces. We use reliable ab initio potentials to model the gas-substrate interactions. Evidence for prewetting transitions is found for all the systems investigated and their wetting phase diagrams are calculated
HE-4-PHONON INTERACTION ON A GRAPHITE SUBSTRATE
No full textWe compute the self energy and lifetimes of a 4He atom coupled to the phonon field of a graphite substrate. The substrate phonons are calculated in the continuum elastic approximation, with appropriate boundary conditions at the surface. The energy shift of the ground state amounts to ≈.5°K at zero temperature. Lifetimes are of the order of 10-10 sec. The main contribution is due to the mixed modes of the substrate
Wetting properties of rare gases on weak substrates
No full textSince the original prediction that liquid He does not wet Cs at low temperatures and the soon after experimental observation of a wetting transition on this system, noble gases on alkalis have become model systems for the study of wetting transitions and of their accompanying line of prewetting transitions off coexistence. Here we review very briefly the theory of wetting and prewetting and discuss some results on the properties of rare gases adsorbed on alkali surfaces obtained with the use of the density functional theory and of accurate adsorbate-substrate potentials
COMPUTER-SIMULATIONS OF EXCESS ELECTRON-TRANSPORT IN NEON
No full textThe behavior of excess electrons in neon gas in a wide range of densities is investigated using molecular-dynamics simulations with a parameter-free interparticle potential. A realistic pseudopotential reproducing the measured electron-Ne low-energy scattering properties is used. A transition from quasi-free behavior to a localized regime where the electron is trapped in a bubblelike cavity is observed as the density is increased beyond a value that is close to the experimental one. The calculated electron mobilities in a wide range of densities are also found to be in reasonable agreement with the experimental data
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