235 research outputs found
Mean-field Phase Diagram of Two-Dimensional Electrons with Disorder in a Weak Magnetic Field
We study two-dimensional interacting electrons in a weak perpendicular
magnetic field with the filling factor and in the presence of a
quenched disorder. In the framework of the Hartree-Fock approximation, we
obtain the mean-field phase diagram for the partially filled highest Landau
level. We find that the CDW state can exist if the Landau level broadening
does not exceed the critical value .
Our analysis of weak crystallization corrections to the mean-field results
shows that these corrections are of the order of and
therefore can be neglected
Shubnikov-de Haas oscillations near the metal-insulator transition in a two-dimensional electron system in silicon
We have studied Shubnikov-de Haas oscillations in a two-dimensional electron
system in silicon at low electron densities. Near the metal-insulator
transition, only "spin" minima of the resistance at Landau-level filling
factors 2, 6, 10, and 14 are seen, while the "cyclotron" minima at filling
factors 4, 8, and 12 disappear. A simple explanation of the observed behavior
requires a giant enhancement of the spin splitting near the metal-insulator
transition.Comment: 4 pages, postscript figures include
Atmospheric lepton fluxes at ultrahigh energies
In order to estimate the possibility to observe exotic physics in a neutrino
telescope, it is essential to first understand the flux of atmospheric
neutrinos, muons and dimuons. We study the production of these leptons by
high-energy cosmic rays. We identify three main sources of muons of energy E >
10^6 GeV: the weak decay of charm and bottom mesons and the electromagnetic
decay of unflavored mesons. Contrary to the standard assumption, we find that
eta mesons, not the prompt decay of charm hadrons, are the dominant source of
atmospheric muons at these energies. We show that, as a consequence, the ratio
between the neutrino and muon fluxes is significantly reduced. For dimuons,
which may be a background for long-lived staus produced near a neutrino
telescope, we find that pairs of E ~ 10^7 GeV forming an angle above 10^-6 rad
are produced through D (80%) or B (10%) meson decay and through Drell-Yan
proceses (10%). The frequency of all these processes has been evaluated using
the jet code PYTHIA.Comment: 10 pages, 4 figures; published versio
Sharp increase of the effective mass near the critical density in a metallic 2D electron system
We find that at intermediate temperatures, the metallic temperature
dependence of the conductivity \sigma(T) of 2D electrons in silicon is
described well by a recent interaction-based theory of Zala et al. (Phys. Rev.
B 64, 214204 (2001)). The tendency of the slope d\sigma/dT to diverge near the
critical electron density is in agreement with the previously suggested
ferromagnetic instability in this electron system. Unexpectedly, it is found to
originate from the sharp enhancement of the effective mass, while the effective
Lande g factor remains nearly constant and close to its value in bulk silicon
Muon Capture on the Proton and Deuteron
By measuring the lifetime of the negative muon in pure protium (hydrogen-1),
the MuCap experiment determines the rate of muon capture on the proton, from
which the proton's pseudoscalar coupling g_p may be inferred. A precision of
15% for g_p has been published; this is a step along the way to a goal of 7%.
This coupling can be calculated precisely from heavy baryon chiral perturbation
theory and therefore permits a test of QCD's chiral symmetry. Meanwhile, the
MuSun experiment is in its final design stage; it will measure the rate of muon
capture on the deuteron using a similar technique. This process can be related
through pionless effective field theory and chiral perturbation theory to other
two-nucleon reactions of astrophysical interest, including proton-proton fusion
and deuteron breakup.Comment: Submitted to the proceedings of the 2007 Advanced Studies Institute
on Symmetries and Spin (SPIN-Praha-2007
Origin of the shadow Fermi surface in Bi-based cuprates
We used angle-resolved photoemission spectroscopy to study the shadow Fermi
surface in one layer Bi2Sr1.6La0.4CuO6+delta and two layer
(Bi,Pb)2Sr2CaCu2O8+delta. We find the shadow band to have the same peakwidth
and dispersion as the main band. In addition, the shadow band/main band
intensity ratio is found to be binding energy independent. Consequently, it is
concluded that the shadow bands in Bi-based HTSC do not originate from
antiferromagnetic interactions but have a structural origin.Comment: 10 pages, 2 figure
Interface electronic states and boundary conditions for envelope functions
The envelope-function method with generalized boundary conditions is applied
to the description of localized and resonant interface states. A complete set
of phenomenological conditions which restrict the form of connection rules for
envelope functions is derived using the Hermiticity and symmetry requirements.
Empirical coefficients in the connection rules play role of material parameters
which characterize an internal structure of every particular heterointerface.
As an illustration we present the derivation of the most general connection
rules for the one-band effective mass and 4-band Kane models. The conditions
for the existence of Tamm-like localized interface states are established. It
is shown that a nontrivial form of the connection rules can also result in the
formation of resonant states. The most transparent manifestation of such states
is the resonant tunneling through a single-barrier heterostructure.Comment: RevTeX4, 11 pages, 5 eps figures, submitted to Phys.Rev.
Charge Screening Effect in Metallic Carbon Nanotubes
Charge screening effect in metallic carbon nanotubes is investigated in a
model including the one-dimensional long-range Coulomb interaction. It is
pointed out that an external charge which is being fixed spatially is screened
by internal electrons so that the resulting object becomes electrically
neutral. We found that the screening length is given by about the diameter of a
nanotube.Comment: 11 pages, 6 figure
Quantum magneto-oscillations in a two-dimensional Fermi liquid
Quantum magneto-oscillations provide a powerfull tool for quantifying
Fermi-liquid parameters of metals. In particular, the quasiparticle effective
mass and spin susceptibility are extracted from the experiment using the
Lifshitz-Kosevich formula, derived under the assumption that the properties of
the system in a non-zero magnetic field are determined uniquely by the
zero-field Fermi-liquid state. This assumption is valid in 3D but, generally
speaking, erroneous in 2D where the Lifshitz-Kosevich formula may be applied
only if the oscillations are strongly damped by thermal smearing and disorder.
In this work, the effects of interactions and disorder on the amplitude of
magneto-oscillations in 2D are studied. It is found that the effective mass
diverges logarithmically with decreasing temperature signaling a deviation from
the Fermi-liquid behavior. It is also shown that the quasiparticle lifetime due
to inelastic interactions does not enter the oscillation amplitude, although
these interactions do renormalize the effective mass. This result provides a
generalization of the Fowler-Prange theorem formulated originally for the
electron-phonon interaction.Comment: 4 pages, 1 figur
Electron scattering in multi-wall carbon-nanotubes
We analyze two scattering mechanisms that might cause intrinsic electronic
resistivity in multi-wall carbon nanotubes: scattering by dopant impurities,
and scattering by inter-tube electron-electron interaction. We find that for
typically doped multi-wall tubes backward scattering at dopants is by far the
dominating effect.Comment: 6 pages, 2 figures, to appear in Phys. Rev.
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