2,304 research outputs found
Three-quark potentials in an effective Polyakov loop model
Three-quark potentials are studied in great details in the three-dimensional
pure gauge theory at finite temperature, for the cases of static
sources in the fundamental and adjoint representations. For this purpose, the
corresponding Polyakov loop model in its simplest version is adopted. The
potentials in question, as well as the conventional quark--anti-quark
potentials, are calculated numerically both in the confinement and
deconfinement phases. Results are compared to available analytical predictions
at strong coupling and in the limit of large number of colors . The
three-quark potential is tested against the expected and laws and
the string tension entering these laws is compared to the conventional
string tension. As a byproduct of this investigation, essential
features of the critical behaviour across the deconfinement transition are
elucidated.Comment: 28 pages, 18 figures, 4 tables; some text and a few references added;
version accepted for publication on Nucl. Phys.
Real-time extraction of growth rates from rotating substrates during molecular-beam epitaxy
We present a method for measuring molecular‐beam epitaxy growth rates in near real‐time on rotating substrates. This is done by digitizing a video image of the reflection high‐energy electron diffraction screen, automatically tracking and measuring the specular spot width, and using numerical techniques to filter the resulting signal. The digitization and image and signal processing take approximately 0.4 s to accomplish, so this technique offers the molecular‐beam epitaxy grower the ability to actively adjust growth times in order to deposit a desired layer thickness. The measurement has a demonstrated precision of approximately 2%, which is sufficient to allow active control of epilayer thickness by counting monolayers as they are deposited. When postgrowth techniques, such as frequency domain analysis, are also used, the reflection high‐energy electron diffraction measurement of layer thickness on rotating substrates improves to a precision of better than 1%. Since all of the components in the system described are commercially available, duplication is straightforward
Metal-Insulator Transition Tuned by External Gates in Hall Systems with Constrictions
The nature of a metal-insulator transition tuned by external gates in quantum
Hall (QH) systems with point constrictions, as reported in recent experiments
of Roddaro et al [1], is examined. We attribute this phenomenon to a splitting
of the integer edge into conducting and insulating stripes, the latter wide
enough to allow for the stability of the edge structure. Inter-channel impurity
scattering and inter-channel Coulomb interactions do not destabilize this
picture.Comment: 4 pages, 6 figure
Critical behavior of 3D Z(N) lattice gauge theories at zero temperature
Three-dimensional lattice gauge theories at zero temperature are
studied for various values of . Using a modified phenomenological
renormalization group, we explore the critical behavior of the generalized
model for . Numerical computations are used to simulate
vector models for for lattices with linear extension up
to . We locate the critical points of phase transitions and establish
their scaling with . The values of the critical indices indicate that the
models with belong to the universality class of the three-dimensional
model. However, the exponent derived from the heat capacity is
consistent with the Ising universality class. We discuss a possible resolution
of this puzzle. We also demonstrate the existence of a rotationally symmetric
region within the ordered phase for all at least in the finite
volume.Comment: 25 pages, 4 figures, 8 table
Interactions suppress Quasiparticle Tunneling at Hall Bar Constrictions
Tunneling of fractionally charged quasiparticles across a two-dimensional
electron system on a fractional quantum Hall plateau is expected to be strongly
enhanced at low temperatures. This theoretical prediction is at odds with
recent experimental studies of samples with weakly-pinched
quantum-point-contact constrictions, in which the opposite behavior is
observed. We argue here that this unexpected finding is a consequence of
electron-electron interactions near the point contact.Comment: 4 page
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