7,259 research outputs found
Compressible Anisotropic States around the Half-Filled Landau Levels
Using the von Neumann lattice formalism, we study compressible anisotropic
states around the half-filled Landau levels in the quantum Hall system. In
these states the unidirectional charge density wave (UCDW) state seems to be
the most plausible state. The charge density profile and Hartree-Fock energy of
the UCDW are calculated self-consistently. The wave length dependence of the
energy for the UCDW is also obtained numerically. We show that the UCDW is
regarded as a collection of the one-dimensional lattice Fermi-gas systems which
extend to the uniform direction. The kinetic energy of the gas system is
generated dynamically from the Coulomb interaction.Comment: 6 pages, 5 figures, accepted version for publication in PR
Duality Relation among Periodic Potential Problems in the Lowest Landau Level
Using a momentum representation of a magnetic von Neumann lattice, we study a
two-dimensional electron in a uniform magnetic field and obtain one-particle
spectra of various periodic short-range potential problems in the lowest Landau
level.We find that the energy spectra satisfy a duality relation between a
period of the potential and a magnetic length. The energy spectra consist of
the Hofstadter-type bands and flat bands. We also study the connection between
a periodic short-range potential problem and a tight-binding model.Comment: 6 pages, 3 figures, final version to appear in PR
Stability of the compressible quantum Hall state around the half-filled Landau level
We study the compressible states in the quantum Hall system using a mean
field theory on the von Neumann lattice. In the lowest Landau level, a kinetic
energy is generated dynamically from Coulomb interaction. The compressibility
of the state is calculated as a function of the filling factor and the
width of the spacer between the charge carrier layer and dopants. The
compressibility becomes negative below a critical value of and the state
becomes unstable at . Within a finite range around , the
stable compressible state exists above the critical value of .Comment: 4 pages, 4 Postscript figures, RevTe
Integer Quantum Hall Effect with Realistic Boundary Condition : Exact Quantization and Breakdown
A theory of integer quantum Hall effect(QHE) in realistic systems based on
von Neumann lattice is presented. We show that the momentum representation is
quite useful and that the quantum Hall regime(QHR), which is defined by the
propagator in the momentum representation, is realized. In QHR, the Hall
conductance is given by a topological invariant of the momentum space and is
quantized exactly. The edge states do not modify the value and topological
property of in QHR. We next compute distribution of current based
on effective action and find a finite amount of current in the bulk and the
edge, generally. Due to the Hall electric field in the bulk, breakdown of the
QHE occurs. The critical electric field of the breakdown is proportional to
and the proportional constant has no dependence on Landau levels in
our theory, in agreement with the recent experiments.Comment: 48 pages, figures not included, some additions and revision
Scalar form factors and nuclear interactions
The scalar-isoscalar term in the two-pion exchange potential is
abnormally large and does not respect the hierarchy of effects predicted by
chiral perturbation theory. We argue that this anomaly is associated with
non-perturbative effects, which are also present in the scalar form
factor.Comment: Talk given at the 20EFB, Pisa, Italy, September 2007. 3 pages and 4
figure
Continuum Annulus Amplitude from the Two-Matrix Model
An explicit expression for continuum annulus amplitudes having boundary
lengths and is obtained from the two-matrix model for the
case of the unitary series; . In the limit of vanishing
cosmological constant, we find an integral representation of these amplitudes
which is reproduced, for the cases of the and the , by a continuum approach consisting of quantum mechanics of loops
and a matter system integrated over the modular parameter of the annulus. We
comment on a possible relation to the unconventional branch of the Liouville
gravity.Comment: 9 pages, OU-HET 190, revised version. A part of the conclusions has
been corrected. A new result on integral representation of the annulus
amplitudes has been adde
Persistence of Covalent Bonding in Liquid Silicon Probed by Inelastic X-ray Scattering
Metallic liquid silicon at 1787K is investigated using x-ray Compton
scattering. An excellent agreement is found between the measurements and the
corresponding Car-Parrinello molecular dynamics simulations. Our results show
persistence of covalent bonding in liquid silicon and provide support for the
occurrence of theoretically predicted liquid-liquid phase transition in
supercooled liquid states. The population of covalent bond pairs in liquid
silicon is estimated to be 17% via a maximally-localized Wannier function
analysis. Compton scattering is shown to be a sensitive probe of bonding
effects in the liquid state.Comment: 5pages, 3 postscript figure
Differential decay rate for semileptonic decays
We present our study on semileptonic decay form factors
with NRQCD action for heavy quark from a quenched lattice QCD simulation at
=5.9 on a lattice. We obtain form factors defined in the
context of heavy quark effective theory by Burdman et al. and find that their
correction is small. The limit of physical heavy and light quark masses
can be performed without introducing any model function, and we obtain a
prediction for the differential decay rate . We also discuss the
soft pion limit of the form factors.Comment: Lattice 2000, 4 pages, 4 figures, Late
Non-perturbative renormalization for a renormalization group improved gauge action
Renormalization constants of vector () and axial-vector () currents
are determined non-perturbatively in quenched QCD for a renormalization group
improved gauge action and a tadpole improved clover quark action using the
Schr\"odinger functional method. Non-perturbative values of and
turn out to be smaller than the one-loop perturbative values by at
GeV. A sizable scaling violation of meson decay constants
and observed with the one-loop renormalization factors remains
even with non-perturbative renormalization.Comment: Lattice2001(improvement), 3 pages, 7 figure
The quantum phase transition of itinerant helimagnets
We investigate the quantum phase transition of itinerant electrons from a
paramagnet to a state which displays long-period helical structures due to a
Dzyaloshinskii instability of the ferromagnetic state. In particular, we study
how the self-generated effective long-range interaction recently identified in
itinerant quantum ferromagnets is cut-off by the helical ordering. We find that
for a sufficiently strong Dzyaloshinskii instability the helimagnetic quantum
phase transition is of second order with mean-field exponents. In contrast, for
a weak Dzyaloshinskii instability the transition is analogous to that in
itinerant quantum ferromagnets, i.e. it is of first order, as has been observed
in MnSi.Comment: 5 pages RevTe
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