4,749 research outputs found
Electron Identification in Belle
We report on electron identification methods and their performance in the
Belle experiment at the KEK-B asymmetric B-Factory storage ring.
Electrons are selected using a likelihood approach that takes information from
the electromagnetic calorimeter, the central drift chamber, and the silica
aerogel Cherenkov counters as input. We achieve an electron identification
efficiency of with a fake rate of for the momentum range between 1.0 GeV/ and 3.0 GeV/ in
laboratory frame.Comment: 20 page
Real-space electronic-structure calculations with full-potential all-electron precision for transition-metals
We have developed an efficient computational scheme utilizing the real-space
finite-difference formalism and the projector augmented-wave (PAW) method to
perform precise first-principles electronic-structure simulations based on the
density functional theory for systems containing transition metals with a
modest computational effort. By combining the advantages of the time-saving
double-grid technique and the Fourier filtering procedure for the projectors of
pseudopotentials, we can overcome the egg box effect in the computations even
for first-row elements and transition metals, which is a problem of the
real-space finite-difference formalism. In order to demonstrate the potential
power in terms of precision and applicability of the present scheme, we have
carried out simulations to examine several bulk properties and structural
energy differences between different bulk phases of transition metals, and have
obtained excellent agreement with the results of other precise first-principles
methods such as a plane wave based PAW method and an all-electron
full-potential linearized augmented plane wave (FLAPW) method.Comment: 29 Page
Molecular beam epitaxial growth of high-quality InSb on InP and GaAs substrates
Epitaxial layers of InSb were grown on InP and GaAs substrates by molecular beam epitaxy. The dependence of the epilayer quality on flux ratio, J sub Sb4/J sub In, was studied. Deviation from an optimum value of J sub Sb4/J sub In (approx. 2) during growth led to deterioration in the surface morphology and the electrical and crystalline qualities of the films. Room temperature electron mobilities as high as 70,000 and 53,000 sq cm /V-s were measured in InSb layers grown on InP and GaAs substrates, respectively. Unlike the previous results, the conductivity in these films is n-type even at T = 13 K, and no degradation of the electron mobility due to the high density of dislocations was observed. The measured electron mobilities (and carrier concentrations) at 77 K in InSb layers grown on InP and GaAs substrates are 110,000 sq cm/V-s (3 x 10(15) cm(-3)) and 55,000 sq cm/V-s (4.95 x 10(15) cm(-3)), respectively, suggesting their application to electronic devices at cryogenic temperatures
Quantum Monte Carlo simulation of S=1/2 Heisenberg model with four spin interaction
25th International Conference on Low Temperature Physics (LT25)The spin S = 1/2 Heisenberg model with four-spin interaction on the square lattice is studied by using quantum Monte Carlo method. When the four-spin interaction is dominant, the system has a VBS ground state. In this case, we find a finite-temperature second-order phase transition to the VBS state. The universality class of the transition is investigated. We estimate the critical exponents ν and η from the finite size scaling analysis and find ν = 0.68(1) and η = 0.55(2)
The spin-incoherent Luttinger liquid
In contrast to the well known Fermi liquid theory of three dimensions,
interacting one-dimensional and quasi one-dimensional systems of fermions are
described at low energy by an effective theory known as Luttinger liquid
theory. This theory is expressed in terms of collective many-body excitations
that show exotic behavior such as spin-charge separation. Luttinger liquid
theory is commonly applied on the premise that "low energy" describes both the
spin and charge sectors. However, when the interactions in the system are very
strong, as they typically are at low particle densities, the ratio of spin to
charge energy may become exponentially small. It is then possible at very low
temperatures for the energy to be low compared to the characteristic charge
energy, but still high compared to the characteristic spin energy. This energy
window of near ground-state charge degrees of freedom, but highly thermally
excited spin degrees of freedom is called a spin-incoherent Luttinger liquid.
The spin-incoherent Luttinger liquid exhibits a higher degree universality than
the Luttinger liquid and its properties are qualitatively distinct. In this
colloquium I detail some of the recent theoretical developments in the field
and describe experimental indications of such a regime in gated semiconductor
quantum wires.Comment: 21 pages, 18 figures. Updated references, corrected typo in Eq.(20)
in journal versio
High Field Anomalies of Equilibrium and Ultrafast Magnetism in Rare-Earth-Transition Metal Ferrimagnets
Magneto-optical spectroscopy in fields up to 30 Tesla reveals anomalies in
the equilibrium and ultrafast magnetic properties of the ferrimagnetic
rare-earth-transition metal alloy TbFeCo. In particular, in the vicinity of the
magnetization compensation temperature, each of the magnetizations of the
antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis
loops. Contrary to state-of-the-art theory, which explains such loops by sample
inhomogeneities, here we show that they are an intrinsic property of the
rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and
have a non-zero orbital momentum in the ground state and, therefore, a large
magnetic anisotropy, we are able to reproduce the experimentally observed
behavior in equilibrium. The same theory is also able to describe the
experimentally observed critical slowdown of the spin dynamics in the vicinity
of the magnetization compensation temperature, emphasizing the role played by
the orbital momentum in static and ultrafast magnetism of ferrimagnets
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