158 research outputs found
Full-analytic frequency-domain 1pN-accurate gravitational wave forms from eccentric compact binaries
The article provides ready-to-use 1pN-accurate frequency-domain gravitational
wave forms for eccentric nonspinning compact binaries of arbitrary mass ratio
including the first post-Newtonian (1pN) point particle corrections to the
far-zone gravitational wave amplitude, given in terms of tensor spherical
harmonics. The averaged equations for the decay of the eccentricity and growth
of radial frequency due to radiation reaction are used to provide stationary
phase approximations to the frequency-domain wave forms.Comment: 28 pages, submitted to PR
Scanning-probe spectroscopy of semiconductor donor molecules
Semiconductor devices continue to press into the nanoscale regime, and new
applications have emerged for which the quantum properties of dopant atoms act
as the functional part of the device, underscoring the necessity to probe the
quantum structure of small numbers of dopant atoms in semiconductors[1-3].
Although dopant properties are well-understood with respect to bulk
semiconductors, new questions arise in nanosystems. For example, the quantum
energy levels of dopants will be affected by the proximity of nanometer-scale
electrodes. Moreover, because shallow donors and acceptors are analogous to
hydrogen atoms, experiments on small numbers of dopants have the potential to
be a testing ground for fundamental questions of atomic and molecular physics,
such as the maximum negative ionization of a molecule with a given number of
positive ions[4,5]. Electron tunneling spectroscopy through isolated dopants
has been observed in transport studies[6,7]. In addition, Geim and coworkers
identified resonances due to two closely spaced donors, effectively forming
donor molecules[8]. Here we present capacitance spectroscopy measurements of
silicon donors in a gallium-arsenide heterostructure using a scanning probe
technique[9,10]. In contrast to the work of Geim et al., our data show
discernible peaks attributed to successive electrons entering the molecules.
Hence this work represents the first addition spectrum measurement of dopant
molecules. More generally, to the best of our knowledge, this study is the
first example of single-electron capacitance spectroscopy performed directly
with a scanning probe tip[9].Comment: In press, Nature Physics. Original manuscript posted here; 16 pages,
3 figures, 5 supplementary figure
Motion and gravitational wave forms of eccentric compact binaries with orbital-angular-momentum-aligned spins under next-to-leading order in spin-orbit and leading order in spin(1)-spin(2) and spin-squared couplings
A quasi-Keplerian parameterisation for the solutions of second post-Newtonian
(PN) accurate equations of motion for spinning compact binaries is obtained
including leading order spin-spin and next-to-leading order spin-orbit
interactions. Rotational deformation of the compact objects is incorporated.
For arbitrary mass ratios the spin orientations are taken to be parallel or
anti-parallel to the orbital angular momentum vector. The emitted gravitational
wave forms are given in analytic form up to 2PN point particle, 1.5PN spin
orbit and 1PN spin-spin contributions, where the spins are counted of 0PN
order.Comment: 26 pages, 1 figure, published in CQG. Current version: we removed a
remark and clarified the derivation of the orbital element \e_ph
Direct observation of micron-scale ordered structure in a two-dimensional electron system
We have applied a novel scanned probe method to directly resolve the interior
structure of a GaAs/AlGaAs two-dimensional electron system in a tunneling
geometry. We find that the application of a perpendicular magnetic field can
induce surprising density modulations that are not static as a function of the
field. Near six and four filled Landau levels, stripe-like structures emerge
with a characteristic wave length ~2 microns. Present theories do not account
for ordered density modulations on this length scale.Comment: 5 pages, 4 figures. To appear in Phys. Rev.
Modifying the surface electronic properties of YBa2Cu3O7-delta with cryogenic scanning probe microscopy
We report the results of a cryogenic study of the modification of
YBa2Cu3O7-delta surface electronic properties with the probe of a scanning
tunneling microscope (STM). A negative voltage applied to the sample during STM
tunneling is found to modify locally the conductance of the native degraded
surface layer. When the degraded layer is removed by etching, the effect
disappears. An additional surface effect is identified using Scanning Kelvin
Probe Microscopy in combination with STM. We observe reversible surface
charging for both etched and unetched samples, indicating the presence of a
defect layer even on a surface never exposed to air.Comment: 6 pages, 4 figures. To appear in Superconductor Science and
Technolog
Electrostatics of Inhomogeneous Quantum Hall Liquid
The distribution of electron density in the quantum Hall liquid is considered
in the presence of macroscopic density gradient caused by side electrodes or
inhomogeneous doping. In this case different Landau levels are occupied in
different regions of a sample. These regions are separated by incompressible
liquid. It is shown that the applicability of the approach by Chklovskii et al.
is substantially restricted if the density gradient is not very large and
disorder is important. Due to the fluctuations of the remote donor's density
the liquid in the transition region can not be considered as completely
incompressible. In the typical situation, when the gap between Landau levels is
not much larger than the energy of disorder, the transition region is a wide
band where electron density, averaged over the fluctuations, is independent of
magnetic field. The band is a random mixture of regions occupied by electrons
of upper level, by holes of lower level and by incompressible liquid. The width
of this band is calculated and an analytical expression for the fraction of
incompressible liquid in different parts of this band is given.Comment: 12 pages, RevTe
Modeling Subsurface Charge Accumulation Images of a Quantum Hall Liquid
Subsurface Charge Accumulation imaging is a cryogenic scanning probe
technique that has recently been used to spatially probe incompressible strips
formed in a two-dimensional electron system (2DES) at high magnetic fields. In
this paper, we present detailed numerical modeling of these data. At a basic
level, the method produces results that agree well with the predictions of
models based on simple circuit elements. Moreover, the modeling method is
sufficiently advanced to simulate the spatially resolved measurements. By
comparing directly the simulations to the experimentally measured data, we can
extract quantitatively local electronic features of the 2DES. In particular, we
deduce the electron density of states inside the incompressible strips and
electrical resistance across them.Comment: 11 pages, 3 figure
Imaging Inter-Edge State Scattering Centers in the Quantum Hall Regime
We use an atomic force microscope tip as a local gate to study the scattering
between edge channels in a 2D electron gas in the quantum Hall regime. The
scattering is dominated by individual, microscopic scattering centers, which we
directly image here for the first time. The tip voltage dependence of the
scattering indicates that tunneling occurs through weak links and localized
states.Comment: 4 pages, 5 figure
Quantum Hall fluctuations and evidence for charging in the quantum Hall effect
We find that mesoscopic conductance fluctuations in the quantum Hall regime
in silicon MOSFETs display simple and striking patterns. The fluctuations fall
into distinct groups which move along lines parallel to loci of integer filling
factor in the gate voltage-magnetic field plane. Also, a relationship appears
between the fluctuations on quantum Hall transitions and those found at low
densities in zero magnetic field. These phenomena are most naturally attributed
to charging effects. We argue that they are the first unambiguous manifestation
of interactions in dc transport in the integer quantum Hall effect.Comment: 4 pages RevTeX including 4 postscript bitmapped figure
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