1,310 research outputs found
Coherent control of magnetization precession in ferromagnetic semiconductor (Ga,Mn)As
We report single-color, time resolved magneto-optical measurements in
ferromagnetic semiconductor (Ga,Mn)As. We demonstrate coherent optical control
of the magnetization precession by applying two successive ultrashort laser
pulses. The magnetic field and temperature dependent experiments reveal the
collective Mn-moment nature of the oscillatory part of the time-dependent Kerr
rotation, as well as contributions to the magneto-optical signal that are not
connected with the magnetization dynamics.Comment: 6 pages, 3 figures, accepted in Applied Physics Letter
Laser-induced Precession of Magnetization in GaMnAs
We report on the photo-induced precession of the ferromagnetically coupled Mn
spins in (Ga,Mn)As, which is observed even with no external magnetic field
applied. We concentrate on various experimental aspects of the time-resolved
magneto-optical Kerr effect (TR-MOKE) technique that can be used to clarify the
origin of the detected signals. We show that the measured data typically
consist of several different contributions, among which only the oscillatory
signal is directly connected with the ferromagnetic order in the sample.Comment: 4 pages, 5 figure
Local Government Fiscal Burden in Nonmetropolitan America
Rising fiscal pressure on local governments in rural areas of the United States is documented in this study. The level of fiscal burden on taxpayers to support local governments in nonmetropolitan areas is found to be higher than that in metropolitan areas between 1977 and 1987. Using a model from the urban fiscal literature, the level of fiscal burden in nonmetropolitan areas is found to be influenced by a combination of demographic, socioeconomic, intergovernmental, and historical factors. Intergovernmental revenue transfers from the state and federal government play a critical role in determining the level of fiscal burden rural taxpayers bear. These findings have implications for rural economic development and for understanding how rural areas are influenced by the larger society
Magnetic Field Effects in the Pseudogap Phase: A Competing Energy Gap Scenario for Precursor Superconductivity
We study the sensitivity of T_c and T^* to low fields, H, within the
pseudogap state using a BCS-based approach extended to arbitrary coupling. We
find that T^* and T_c, which are of the same superconducting origin, have very
different H dependences. This is due to the pseudogap, \Delta_{pg}, which is
present at the latter, but not former temperature. Our results for the
coherence length \xi fit well with existing experiments.We predict that very
near the insulator \xi will rapidly increase.Comment: 4 pages, 4 figures, RevTe
Oxidation and reduction kinetics of eutectic SnPb, InSn, and AuSn: a knowledge base for fluxless solder bonding applications
Light-induced magnetization precession in GaMnAs
We report dynamics of the transient polar Kerr rotation (KR) and of the
transient reflectivity induced by femtosecond laser pulses in ferromagnetic
(Ga,Mn)As with no external magnetic field applied. It is shown that the
measured KR signal consist of several different contributions, among which only
the oscillatory signal is directly connected with the ferromagnetic order in
(Ga,Mn)As. The origin of the light-induced magnetization precession is
discussed and the magnetization precession damping (Gilbert damping) is found
to be strongly influenced by annealing of the sample.Comment: 6 pages, 4 figures. accepted in Applied Physics Letter
Coulomb Correlations and Pseudo-gap Effects in a Pre-formed Pair Model for the Cuprates
We extend previous work on pre-formed pair models of superconductivity to
incorporate Coulomb correlation effects. For neutral systems, these models have
provided a useful scheme which interpolates between BCS and Bose Einstein
condensation with increasing coupling and thereby describes some aspects of
pseudo-gap phenomena. However, charge fluctuations (via the plasmon,
) significantly modify the collective modes and therefore the
interpolation behavior. We discuss the resulting behavior of the pseudo-gap and
thermodynamic quantities such as , and as a function of
.Comment: 4 pages RevTeX, 3 ps figures included (Submitted to Physical Review B
August 27, 1996
Superconducting phase coherence in the presence of a pseudogap: Relation to specific heat, tunneling and vortex core spectroscopies
In this paper we demonstrate how, using a natural generalization of BCS
theory, superconducting phase coherence manifests itself in phase insensitive
measurements, when there is a smooth evolution of the excitation gap \Delta
from above to below Tc. In this context, we address the underdoped cuprates.
Our premise is that just as Fermi liquid theory is failing above Tc, BCS theory
is failing below. The order parameter \Delta_{sc} is different from the
excitation gap \Delta. Equivalently there is a (pseudo)gap in the excitation
spectrum above Tc which is also present in the underlying normal state of the
superconducting phase, and can be directly inferred from specific heat and
vortex core experiments. At the same time many features of BCS theory, e.g.,
fermionic quasiparticles below Tc, are clearly present. These observations can
be reconciled by a natural extension of BCS theory, which includes finite
center-of-mass momentum pair excitations, in addition to the usual fermionic
quasiparticles. Applying this theory we find that the Bose condensation of
Cooper pairs, which is reflected in \Delta_{sc}, leads to sharp peaks in the
spectral function once . These are manifested in ARPES spectra as
well as in specific heat jumps, which become more like the behavior in a
\lambda transition as the pseudogap develops. We end with a discussion of
tunneling experiments and condensation energy issues. Comparison between
theoretical and experimental plots of C_v, and of tunneling and vortex core
spectroscopy measurements is good.Comment: 12 pages, 8 figures, ReVTeX 3.
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