17,382 research outputs found
Magnetic incommensurability in -type cuprate perovskites
For the superconducting phase with a d-wave order parameter and zero
temperature the magnetic susceptibility of the t-J model is calculated using
the Mori projection operator technique. Conditions for the appearance of an
incommensurate magnetic response below the resonance frequency are identified.
A fast decay of the tails of the hole coherent peaks and a weak intensity of
the hole incoherent continuum near the Fermi level are enough to produce an
incommensurate response using different hole dispersions established for
-type cuprates, in which such response was observed. In this case, the
nesting of the itinerant-electron theory or the charge modulation of the stripe
theory is unnecessary for the incommensurability. The theory reproduces the
hourglass dispersion of the susceptibility maxima with their location in the
momentum space similar to that observed experimentally. The upper branch of the
dispersion stems from the excitations of localized spins, while the lower one
is due to the incommensurate maxima of their damping. The narrow and intensive
resonance peak arises if the frequency of these excitations at the
antiferromagnetic momentum lies below the edge of the two-fermion continuum;
otherwise the maximum is broad and less intensive.Comment: 22 pages, 7 figure
Updated, expanded, fluid properties handbook
Revised handbook presents quantitative data, in the form of graphs and charts, pertaining to thermodynamic properties of specific cryogenic fluids and several metals. References to sources of data are cited
Coherent Excitation of the 6S1/2 to 5D3/2 Electric Quadrupole Transition in 138Ba+
The electric dipole-forbidden, quadrupole 6S1/2 5D3/2 transition in Ba+
near 2051 nm, with a natural linewidth of 13 mHz, is attractive for potential
observation of parity non-conservation, and also as a clock transition for a
barium ion optical frequency standard. This transition also offers a direct
means of populating the metastable 5D3/2 state to measure the nuclear magnetic
octupole moment in the odd barium isotopes. Light from a diode-pumped, solid
state Tm,Ho:YLF laser operating at 2051 nm is used to coherently drive this
transition between resolved Zeeman levels in a single trapped 138Ba+ ion. The
frequency of the laser is stabilized to a high finesse Fabry Perot cavity at
1025 nm after being frequency doubled. Rabi oscillations on this transition
indicate a laser-ion coherence time of 3 ms, most likely limited by ambient
magnetic field fluctuations.Comment: 5 pages, 5 figure
A magnetogasdynamic power generation study third quarterly progress report
Calculations of preionized plasma flow with finite recombination rate - magnetohydrodynamic power generator stud
Spin-orbital phase synchronization in the magnetic field-driven electron dynamics in a double quantum dot
We study the dynamics of an electron confined in a one-dimensional double
quantum dot in the presence of driving external magnetic fields. The orbital
motion of the electron is coupled to the spin dynamics by spin orbit
interaction of the Dresselhaus type. We derive an effective time-dependent
Hamiltonian model for the orbital motion of the electron and obtain a
synchronization condition between the orbital and the spin dynamics. From this
model we deduce an analytical expression for the Arnold tongue and propose an
experimental scheme for realizing the synchronization of the orbital and spin
dynamics.Comment: 6 figures, 14 page
Resonance peak in underdoped cuprates
The magnetic susceptibility measured in neutron scattering experiments in
underdoped YBaCuO is interpreted based on the self-consistent
solution of the t-J model of a Cu-O plane. The calculations reproduce correctly
the frequency and momentum dependencies of the susceptibility and its variation
with doping and temperature in the normal and superconducting states. This
allows us to interpret the maximum in the frequency dependence -- the resonance
peak -- as a manifestation of the excitation branch of localized Cu spins and
to relate the frequency of the maximum to the size of the spin gap. The
low-frequency shoulder well resolved in the susceptibility of superconducting
crystals is connected with a pronounced maximum in the damping of the spin
excitations. This maximum is caused by intense quasiparticle peaks in the hole
spectral function for momenta near the Fermi surface and by the nesting.Comment: 9 pages, 6 figure
Aquila X--1: a low inclination soft X-ray transient
We have obtained I-band photometry of the neutron star X-ray transient Aql
X--1 during quiescence. We find a periodicity at 2.487 cd-1, which we interpret
as twice the orbital frequency (19.30+/-0.05 h). Folding the data on the
orbital period, we model the light curve variations as the ellipsoidal
modulation of the secondary star. We determine the binary inclination to be
20--31 degrees (90 per cent confidence) and also 95 per cent upper limits to
the radial velocity semi-amplitude and rotational broadening of the secondary
star to be 117 kms-1 and 50 kms-1 respectively.Comment: 4 pages text, 3 figures, to appear in MNRA
Low-frequency incommensurate magnetic response in strongly correlated systems
It is shown that in the t-J model of Cu-O planes at low frequencies the
dynamic spin structure factor is peaked at incommensurate wave vectors
(1/2+-delta,1/2)$, (1/2,1/2+-delta). The incommensurability is connected with
the momentum dependencies of the magnon frequency and damping near the
antiferromagnetic wave vector. The behavior of the incommensurate peaks is
similar to that observed in La_{2-x}(Ba,Sr)_xCuO_{4+y} and YBa_2Cu_3O_{7-y}:
for hole concentrations 0.02<x<=0.12 we find that delta is nearly proportional
to x, while for x>0.12 it tends to saturation. The incommensurability
disappears with increasing temperature. Generally the incommensurate magnetic
response is not accompanied by an inhomogeneity of the carrier density.Comment: 4 pages, 4 figure
Reversible strain effect on the magnetization of LaCoO3 films
The magnetization of ferromagnetic LaCoO3 films grown epitaxially on
piezoelectric substrates has been found to systematically decrease with the
reduction of tensile strain. The magnetization change induced by the reversible
strain variation reveals an increase of the Co magnetic moment with tensile
strain. The biaxial strain dependence of the Curie temperature is estimated to
be below 4K/% in the as-grown tensile strain state of our films. This is in
agreement with results from statically strained films on various substrates
- …