583 research outputs found
Curve crossing in linear potential grids: the quasidegeneracy approximation
The quasidegeneracy approximation [V. A. Yurovsky, A. Ben-Reuven, P. S.
Julienne, and Y. B. Band, J. Phys. B {\bf 32}, 1845 (1999)] is used here to
evaluate transition amplitudes for the problem of curve crossing in linear
potential grids involving two sets of parallel potentials. The approximation
describes phenomena, such as counterintuitive transitions and saturation
(incomplete population transfer), not predictable by the assumption of
independent crossings. Also, a new kind of oscillations due to quantum
interference (different from the well-known St\"uckelberg oscillations) is
disclosed, and its nature discussed. The approximation can find applications in
many fields of physics, where multistate curve crossing problems occur.Comment: LaTeX, 8 pages, 8 PostScript figures, uses REVTeX and psfig,
submitted to Physical Review
Insulator-Metal Transition in the One and Two-Dimensional Hubbard Models
We use Quantum Monte Carlo methods to determine Green functions,
, on lattices up to for the 2D Hubbard model
at . For chemical potentials, , within the Hubbard gap, , and at {\it long} distances, , with critical behavior: , . This result stands in agreement with the
assumption of hyperscaling with correlation exponent and dynamical
exponent . In contrast, the generic band insulator as well as the
metal-insulator transition in the 1D Hubbard model are characterized by and .Comment: 9 pages (latex) and 5 postscript figures. Submitted for publication
in Phys. Rev. Let
Counterintuitive transitions in the multistate Landau-Zener problem with linear level crossings
We generalize the Brundobler-Elser hypothesis in the multistate Landau-Zener
problem to the case when instead of a state with the highest slope of the
diabatic energy level there is a band of states with an arbitrary number of
parallel levels having the same slope. We argue that the probabilities of
counterintuitive transitions among such states are exactly zero.Comment: 9 pages, 5 figure
Thermodynamics of doped Kondo insulator in one dimension: Finite Temperature DMRG Study
The finite-temperature density-matrix renormalization-group method is applied
to the one-dimensional Kondo lattice model near half filling to study its
thermodynamics. The spin and charge susceptibilities and entropy are calculated
down to T=0.03t. We find two crossover temperatures near half filling. The
higher crossover temperature continuously connects to the spin gap at half
filling, and the susceptibilities are suppressed around this temperature. At
low temperatures, the susceptibilities increase again with decreasing
temperature when doping is finite. We confirm that they finally approach to the
values obtained in the Tomonaga-Luttinger (TL) liquid ground state for several
parameters. The crossover temperature to the TL liquid is a new energy scale
determined by gapless excitations of the TL liquid. The transition from the
metallic phase to the insulating phase is accompanied by the vanishing of the
lower crossover temperature.Comment: 4 pages, 7 Postscript figures, REVTe
Electrical Conductivity of Fermi Liquids. I. Many-body Effect on the Drude Weight
On the basis of the Fermi liquid theory, we investigate the many-body effect
on the Drude weight. In a lattice system, the Drude weight is modified by
electron-electron interaction due to Umklapp processes, while it is not
renormalized in a Galilean invariant system. This is explained by showing that
the effective mass for is defined through the current, not
velocity, of quasiparticle. It is shown that the inequality is required
for the stability against the uniform shift of the Fermi surface. The result of
perturbation theory applied for the Hubbard model indicates that as a
function of the density is qualitatively modified around half filling
by Umklapp processes.Comment: 20 pages, 2 figures; J. Phys. Soc. Jpn. Vol.67, No.
Resonance Patterns of an Antidot Cluster: From Classical to Quantum Ballistics
We explain the experimentally observed Aharonov-Bohm (AB) resonance patterns
of an antidot cluster by means of quantum and classical simulations and Feynman
path integral theory. We demonstrate that the observed behavior of the AB
period signals the crossover from a low B regime which can be understood in
terms of electrons following classical orbits to an inherently quantum high B
regime where this classical picture and semiclassical theories based on it do
not apply.Comment: 5 pages revtex + 2 postscript figure
Cyclization of a carbon-centered radical derived from oxaziridine cleavage
Treatment of an oxaziridine with low-valent iron or copper salts generates a carbon-centered radical able to cyclize onto an appended olefin
Few-electron molecular states and their transitions in a single InAs quantum dot molecule
We study electronic configurations in a single pair of vertically coupled
self-assembled InAs quantum dots, holding just a few electrons. By comparing
the experimental data of non-linear single-electron transport spectra in a
magnetic field with many-body calculations, we identify the spin and orbital
configurations to confirm the formation of molecular states by filling both the
quantum mechanically coupled symmetric and anti-symmetric states. Filling of
the anti-symmetric states is less favored with increasing magnetic field, and
this leads to various magnetic field induced transitions in the molecular
states.Comment: 14 pages, 3 figures, Accepted for publication in Phys. Rev. Let
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