7,145 research outputs found
Pulse-pumped double quantum dot with spin-orbit coupling
We consider the full driven quantum dynamics of a qubit realized as spin of
electron in a one-dimensional double quantum dot with spin-orbit coupling. The
driving perturbation is taken in the form of a single half-period pulse of
electric field. Spin-orbit coupling leads to a nontrivial evolution in the spin
and charge densities making the dynamics in both quantities irregular. As a
result, the charge density distribution becomes strongly spin-dependent. The
transition from the field-induced tunneling to the strong coupling regime is
clearly seen in the charge and spin channels. These results can be important
for the understanding of the techniques for the spin manipulation in
nanostructures.Comment: 6 figure
Low-Frequency Quantum Oscillations due to Strong Electron Correlations
The normal-state energy spectrum of the two-dimensional - model in a
homogeneous perpendicular magnetic field is investigated. The density of states
at the Fermi level as a function of the inverse magnetic field
reveals oscillations in the range of hole concentrations . The
oscillations have both high- and low-frequency components. The former
components are connected with large Fermi surfaces, while the latter with van
Hove singularities in the Landau subbands, which traverse the Fermi level with
changing . The singularities are related to bending the Landau subbands due
to strong electron correlations. Frequencies of these components are of the
same order of magnitude as quantum oscillation frequencies observed in
underdoped cuprates.Comment: 10 pages, 3 figures, Proc. NSS-2013, Yalta. arXiv admin note: text
overlap with arXiv:1308.056
Piezoelectric mechanism of orientation of a bilayer Wigner crystal in a GaAs matrix
A mechanism for orientation of bilayer classical Wigner crystals in a
piezoelectric medium is considered. For the GaAs system the piezoelectric
correction to the electrostatic interaction between electrons is calculated. It
is shown that taking into account the correction due to the piezoelectric
effect leads to a dependence of the total energy of the electron crystal on its
orientation with respect to the crystallographic axes of the surrounding
matrix. A generalization of Ewald's method is obtained for calculating the
anisotropic interaction between electrons in a Wigner crystal. The method is
used to calculate the energy of bilayer Wigner crystals in electron layers
parallel to the crystallographic planes (001), (0-11), and (111) as a function
of their orientation and the distance between layers, and the energetically
most favorable orientation for all types of electron lattices in a bilayer
system is found. It is shown that phase transitions between structures with
different lattice symmetry in a Wigner crystal can be accompanied by a change
of its orientation.Comment: 11 pages, 4 eps figures include
Temperature behavior of the magnon modes of the square lattice antiferromagnet
A spin-wave theory of short-range order in the square lattice Heisenberg
antiferromagnet is formulated. With growing temperature from T=0 a gapless mode
is shown to arise simultaneously with opening a gap in the conventional
spin-wave mode. The spectral intensity is redistributed from the latter mode to
the former. For low temperatures the theory reproduces results of the modified
spin-wave theory by M.Takahashi, J.E.Hirsch et al. and without fitting
parameters gives values of observables in good agreement with Monte Carlo
results in the temperature range 0 <= T < 0.8J where J is the exchange
constant.Comment: 12 pages, 2 figure
Suppression of the ferromagnetic state in LaCoO3 films by rhombohedral distortion
Epitaxially strained LaCoO3 (LCO) thin films were grown with different film
thickness, t, on (001) oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT)
substrates. After initial pseudomorphic growth the films start to relieve their
strain partly by the formation of periodic nano-twins with twin planes
predominantly along the direction. Nano-twinning occurs already at the
initial stage of growth, albeit in a more moderate way. Pseudomorphic grains,
on the other hand, still grow up to a thickness of at least several tenths of
nanometers. The twinning is attributed to the symmetry lowering of the
epitaxially strained pseudo-tetragonal structure towards the relaxed
rhombohedral structure of bulk LCO. However, the unit-cell volume of the
pseudo-tetragonal structure is found to be nearly constant over a very large
range of t. Only films with t > 130 nm show a significant relaxation of the
lattice parameters towards values comparable to those of bulk LCO.Comment: 31 pages, 10 figure
Evidence for ammonium-bearing minerals in Ceres
Evidence for ammonium-bearing minerals was found on the surface of the largest asteroid Ceres. The presence of ammonium-bearing clays suggests that Ceres has experienced a period of alteration by substantial amounts of an ammonium-bearing fluid. The presence of the ammonium-bearing clays does not preclude Ceres maintaining a volatile inventory in the core or in a volatile-rich zone at some distance below the surface. Telescopic observations of Ceres, using the 3.0 meter NASA Infrared telescope facility prompted this reevaluation of its surface mineralogy
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