60,489 research outputs found
Magnetic Excitations of Stripes Near a Quantum Critical Point
We calculate the dynamical spin structure factor of spin waves for weakly
coupled stripes. At low energy, the spin wave cone intensity is strongly peaked
on the inner branches. As energy is increased, there is a saddlepoint followed
by a square-shaped continuum rotated 45 degree from the low energy peaks. This
is reminiscent of recent high energy neutron scattering data on the cuprates.
The similarity at high energy between this semiclassical treatment and quantum
fluctuations in spin ladders may be attributed to the proximity of a quantum
critical point with a small critical exponent .Comment: 4+ pages, 5 figures, published versio
Magnetic Excitations of Stripes and Checkerboards in the Cuprates
We discuss the magnetic excitations of well-ordered stripe and checkerboard
phases, including the high energy magnetic excitations of recent interest and
possible connections to the "resonance peak" in cuprate superconductors. Using
a suitably parametrized Heisenberg model and spin wave theory, we study a
variety of magnetically ordered configurations, including vertical and diagonal
site- and bond-centered stripes and simple checkerboards. We calculate the
expected neutron scattering intensities as a function of energy and momentum.
At zero frequency, the satellite peaks of even square-wave stripes are
suppressed by as much as a factor of 34 below the intensity of the main
incommensurate peaks. We further find that at low energy, spin wave cones may
not always be resolvable experimentally. Rather, the intensity as a function of
position around the cone depends strongly on the coupling across the stripe
domain walls. At intermediate energy, we find a saddlepoint at for
a range of couplings, and discuss its possible connection to the "resonance
peak" observed in neutron scattering experiments on cuprate superconductors. At
high energy, various structures are possible as a function of coupling strength
and configuration, including a high energy square-shaped continuum originally
attributed to the quantum excitations of spin ladders. On the other hand, we
find that simple checkerboard patterns are inconsistent with experimental
results from neutron scattering.Comment: 11 pages, 13 figures, for high-res figs, see
http://physics.bu.edu/~yaodx/spinwave2/spinw2.htm
Thermionic research and development program Final report
Rhenium electrode material investigation and performance studies of low temperature cesium vapor thermionic converter
Thermionic research and development program Final report, 15 Jul. 1966 - 15 Jan. 1968
Thermionic research and development program - improvement of performance of low emitter temperature cesium vapor thermionic converter
High-performance thermionic converter Quarterly progress report, 13 Aug. - 13 Nov. 1965
Fabrication and testing of cesium loaded thermionic converter test vehicl
Micromagnetic Domain Structures in Cylindrical Nickel Dots
The magnetic domain structures of cylindrical nickel dots (diameters from 40 nm to 1700 nm) with anisotropy parallel to the cylinder axis is predicted by the ratio of the dot diameter to the stripe period of unpatterned films with the same perpendicular anisotropy. The dominant domain structure for a given ratio increases in complexity as the ratio increases. We present evidence for the full micromagnetic domain structure for the simplest cases
Kink-antikink interactions in the double sine-Gordon equation and the problem of resonance frequencies
We studied the kink-antikink collision process for the "double sine-Gordon"
(DSG) equation in 1+1 dimensions at different values of the potential parameter
. For small values of we discuss the problem of resonance frequencies.
We give qualitative explanation of the frequency shift in comparison with the
frequency of the discrete level in the potential well of isolated kink. We show
that in this region of the parameter the effective long-range interaction
between kink and antikink takes place.Comment: 9 pages, LaTeX, 4 figures (eps
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