14,617 research outputs found
Magnetic properties of Fe/Cu multilayers prepared using pulsed-current electrodeposition
[Fe (tFe) nm/Cu (tCu) nm]N multilayer films were prepared using pulsed-current electrodeposition method. The role of the pulsed-current deposition and Fe and Cu layer thicknesses on the magnetic properties was investigated. The microstructure of the multilayer films is dependent on the thicknesses of both the Fe and Cu layers. The saturation magnetization of the multilayers strongly correlated with the crystalline structure of Fe at the interface of Fe and Cu layers.
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Spontaneous magnetization and structure formation in a spin-1 ferromagnetic Bose-Einstein condensate
Motivated by recent experiments involving the non-destructive imaging of
magnetization of a spin-1 87Rb Bose gas (Higbie et al., cond-mat/0502517), we
address the question of how the spontaneous magnetization of a ferromagnetic
BEC occurs in a spin-conserving system. Due to competition between the
ferromagnetic interaction and the total spin conservation, various spin
structures such as staggered magnetic domains, and helical and concentric ring
structures are formed, depending on the geometry of the trapping potential.Comment: 8 pages, 5 figure
Diagnostics for the ground state phase of a spin-2 Bose-Einstein condensate
We propose a method to determine the singlet-pair energy of a spin-2
Bose-Einstein condensate (BEC). By preparing the initial populations in the
magnetic sublevels 0, 2, -2 with appropriate relative phases, we can obtain the
coefficient of the spin singlet-pair term from the spin exchange dynamics. This
method is suitable for hyperfine states with short lifetimes, since only the
initial change in the population of each magnetic sublevel is needed. This
method therefore enables the determination of the ground state phase of a
spin-2 87Rb BEC at zero magnetic field, which is considered to lie in the
immediate vicinity of the boundary between the antiferromagnetic and cyclic
phases. We also show that the initial state in which relative phases are
controlled can be prepared by Raman processes.Comment: 12 pages, 6 figure
Resonant tunneling and Fano resonance in quantum dots with electron-phonon interaction
We theoretically study the resonant tunneling and Fano resonance in quantum
dots with electron-phonon (e-ph) interaction. We examine the bias-voltage ()
dependence of the decoherence, using Keldysh Green function method and
perturbation with respect to the e-ph interaction. With optical phonons of
energy , only the elastic process takes place when , in
which electrons emit and absorb phonons virtually. The process suppresses the
resonant amplitude. When , the inelastic process is possible which
is accompanied by real emission of phonons. It results in the dephasing and
broadens the resonant width. The bias-voltage dependence of the decoherence
cannot be obtained by the canonical transformation method to consider the e-ph
interaction if its effect on the tunnel coupling is neglected. With acoustic
phonons, the asymmetric shape of the Fano resonance grows like a symmetric one
as the bias voltage increases, in qualitative accordance with experimental
results.Comment: 28 pages, 11 figure
Hermitian conjugate measurement
We propose a new class of probabilistic reversing operations on the state of
a system that was disturbed by a weak measurement. It can approximately recover
the original state from the disturbed state especially with an additional
information gain using the Hermitian conjugate of the measurement operator. We
illustrate the general scheme by considering a quantum measurement consisting
of spin systems with an experimentally feasible interaction and show that the
reversing operation simultaneously increases both the fidelity to the original
state and the information gain with such a high probability of success that
their average values increase simultaneously.Comment: 26 pages, 4 figures; a paragraph is added in the introductio
Pressure-induced changes in the optical properties of quasi-one-dimensional -NaVO
The pressure-induced changes in the optical properties of
-NaVO single crystals at room temperature were studied
by polarization-dependent Raman and far-infrared reflectivity measurements
under high pressure. From the changes in the Raman- and infrared-active phonon
modes in the pressure range 9 - 12 GPa a transfer of charge between the
different V sites can be inferred. The importance of electron-phonon coupling
in the low-pressure regime is discussed.Comment: 7 pages, 5 figure
The dynamics of condensate shells: collective modes and expansion
We explore the physics of three-dimensional shell-shaped condensates,
relevant to cold atoms in "bubble traps" and to Mott insulator-superfluid
systems in optical lattices. We study the ground state of the condensate
wavefunction, spherically-symmetric collective modes, and expansion properties
of such a shell using a combination of analytical and numerical techniques. We
find two breathing-type modes with frequencies that are distinct from that of
the filled spherical condensate. Upon trap release and subsequent expansion, we
find that the system displays self-interference fringes. We estimate
characteristic time scales, degree of mass accumulation, three-body loss, and
kinetic energy release during expansion for a typical system of Rb87
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