8,225 research outputs found
Adsorption and two-body recombination of atomic hydrogen on He-He mixture films
We present the first systematic measurement of the binding energy of
hydrogen atoms to the surface of saturated He-He mixture films.
is found to decrease almost linearly from 1.14(1) K down to 0.39(1) K, when the
population of the ground surface state of He grows from zero to
cm, yielding the value K cm
for the mean-field parameter of H-He interaction in 2D. The experiments
were carried out with overall He concentrations ranging from 0.1 ppm to 5 %
as well as with commercial and isotopically purified He at temperatures
70...400 mK. Measuring by ESR the rate constants and for
second-order recombination of hydrogen atoms in hyperfine states and we
find the ratio to be independent of the He content and to
grow with temperature.Comment: 4 pages, 4 figures, all zipped in a sigle file. Submitted to Phys.
Rev. Let
Universal low-energy properties of three two-dimensional particles
Universal low-energy properties are studied for three identical bosons
confined in two dimensions. The short-range pair-wise interaction in the
low-energy limit is described by means of the boundary condition model. The
wave function is expanded in a set of eigenfunctions on the hypersphere and the
system of hyper-radial equations is used to obtain analytical and numerical
results. Within the framework of this method, exact analytical expressions are
derived for the eigenpotentials and the coupling terms of hyper-radial
equations. The derivation of the coupling terms is generally applicable to a
variety of three-body problems provided the interaction is described by the
boundary condition model. The asymptotic form of the total wave function at a
small and a large hyper-radius is studied and the universal logarithmic
dependence in the vicinity of the triple-collision point is
derived. Precise three-body binding energies and the scattering length
are calculated.Comment: 30 pages with 13 figure
The nonlinear effects in 2DEG conductivity investigation by an acoustic method
The parameters of two-dimensional electron gas (2DEG) in a GaAs/AlGaAs
heterostructure were determined by an acoustical (contactless) method in the
delocalized electrons region (2.5T). Nonlinear effects in Surface
Acoustic Wave (SAW) absorption by 2DEG are determined by the electron heating
in the electric field of SAW, which may be described in terms of electron
temperature . The energy relaxation time is determined
by the scattering at piezoelectric potential of acoustic phonons with strong
screening. At different SAW frequencies the heating depends on the relationship
between and 1 and is determined either by the
instantaneously changing wave field (), or by the
average wave power ().Comment: RevTeX, 5 pages, 3 PS-figures, submitted to Physica Status
Sol.(Technical corrections in PS-figs
Theory of hopping conduction in arrays of doped semiconductor nanocrystals
The resistivity of a dense crystalline array of semiconductor nanocrystals
(NCs) depends in a sensitive way on the level of doping as well as on the NC
size and spacing. The choice of these parameters determines whether electron
conduction through the array will be characterized by activated
nearest-neighbor hopping or variable-range hopping (VRH). Thus far, no general
theory exists to explain how these different behaviors arise at different
doping levels and for different types of NCs. In this paper we examine a simple
theoretical model of an array of doped semiconductor NCs that can explain the
transition from activated transport to VRH. We show that in sufficiently small
NCs, the fluctuations in donor number from one NC to another provide sufficient
disorder to produce charging of some NCs, as electrons are driven to vacate
higher shells of the quantum confinement energy spectrum. This
confinement-driven charging produces a disordered Coulomb landscape throughout
the array and leads to VRH at low temperature. We use a simple computer
simulation to identify different regimes of conduction in the space of
temperature, doping level, and NC diameter. We also discuss the implications of
our results for large NCs with external impurity charges and for NCs that are
gated electrochemically.Comment: 14 pages, 10 figures; extra schematic figures added; revised
introductio
- …