1,345 research outputs found
N\'eel and singlet RVB orders in the t-J model
The N\'eel and the singlet RVB orders of the {\it t-J} model in a 2D square
lattice are studied in the slave-boson mean-field approximation. It is shown
that the N\'eel order parameter takes the maximum value at the finite
temperature and disappear at the lower temperature for a certain range of
doping. It is also shown that the N\'eel and the singlet RVB orders coexist at
low temperature. This suggests the possibility of the coexistence of the N\'eel
and the superconducting orders.Comment: RevTeX, 8 pages, 1 postscript figure. To appear in Physica C, Volume
257, issue 38
Dynamical frictional phenomena in an incommensurate two-chain model
Dynamical frictional phenomena are studied theoretically in a two-chain model
with incommensurate structure. A perturbation theory with respect to the
interchain interaction reveals the contributions from phonons excited in each
chain to the kinetic frictional force. The validity of the theory is verified
in the case of weak interaction by comparing with numerical simulation. The
velocity and the interchain interaction dependences of the lattice structure
are also investigated. It is shown that peculiar breaking of analyticity states
appear, which is characteristic to the two-chain model. The range of the
parameters in which the two-chain model is reduced to the Frenkel-Kontorova
model is also discussed.Comment: RevTex, 9 pages, 7 PostScript figures, to appear in Phys. Rev.
Effect of Local Inhomogeneity on Nucleation; Case of Charge Density Wave Depinning
The spatial inhomogeneities are expected to affect nucleation process in an
essential way. These effects are studied theoretically by considering the case
of the depinning of the charge density wave as a typical example. The threshold
field of the depinning of the one-dimensional commensurate charge density wave
with one impurity has been examined classically based on the phase Hamiltonian
at absolute zero. It is found that the threshold field is lowered by a finite
amount compared to that in the absence of an impurity.Comment: pages 12, LaTeX, 9 figures, uses jpsj.sty, submitted to J. Phys. Soc.
Jp
Stretched exponential behavior in remanent lattice striction of a (La,Pr)SrMnO bilayer manganite single crystal
We have investigated the time dependence of remanent magnetostriction in a
(La,Pr)SrMnO single crystal, in order to examine
the slow dynamics of lattice distortion in bilayered manganites. A competition
between double exchange and Jahn-Teller type orbital-lattice interactions
results in the observed lattice profile following a stretched exponential
function. This finding suggests that spatial growth of the local lattice
distortions coupled with e-electron orbital strongly correlates with the
appearance of the field-induced CMR effect.Comment: 3 figure
Friction, order, and transverse pinning of a two-dimensional elastic lattice under periodic and impurity potentials
Frictional phenomena of two-dimensional elastic lattices are studied
numerically based on a two-dimensional Frenkel-Kontorova model with impurities.
It is shown that impurities can assist the depinning. We also investigate
anisotropic ordering and transverse pinning effects of sliding lattices, which
are characteristic of the moving Bragg glass state and/or transverse glass
state. Peculiar velocity dependence of the transverse pinning is observed in
the presence of both periodic and random potentials and discussed in the
relation with growing order and discommensurate structures.Comment: RevTeX, 4 pages, 5 figures. to appear in Phys. Rev. B Rapid Commu
Effect of suppression of local distortion on magnetic, electrical and thermal transport properties of Cr substituted bi-layer manganite LaSrMnO
We have investigated magnetic, electrical and thermal transport properties
(Seebeck effect and thermal conductivity) of
LaSrMnCrO polycrystalline samples (=0.1, 0.2, 0.4
and 0.6). The Cr substitution for Mn sites causes a removal of
orbital of -electron resulting in a volume shrinkage of
lattice. Magnetic measurements reveal the appearance of a glassy behavior for
Cr-doped samples, accompanied by both a collapse of the A-type
antiferromagnetic structure and the growth of ferromagnetic clusters. Cr-doping
effect on electrical transport strongly enhances an insulating behavior over a
wide range of temperature, while it suppresses a local minimum of
thermoelectric power at lower temperatures. The phonon thermal conduction
gradually rises with increasing Cr content, which is contradictory to a typical
impurity effect on thermal conductivity. We attribute this to a suppression of
local lattice distortion through the introduction of Jahn-Teller inactive ions
of Cr.Comment: 8 pages, 9figure
Anisotropic phonon conduction and lattice distortions in CMR-type bilayer manganite (LaPr)SrMnO (z=0,0.2,0.4 and 0.6) single crystals
We have undertaken a systematic study of thermal conductivity as a function
of temperature and magnetic field of single crystals of the compound
(LaPr)SrMnO for (Pr) =0.2,0.4. and
0.6. The lattice distortion due to Pr-substitution and anisotropic thermal
conductivity in bilayer manganites are discussed on the basis of different
relaxation models of local lattice distortions in metal and insulating states
proposed by Maderda et al. The giant magnetothermal effect is scaled as a
function of magnetization and discussed on the basis of a systematic variation
of the occupation of the -electron orbital states due to Pr-substitution.Comment: 7 pages, 6 figures, in press in Phys.Rev.
The human fear-circuitry and fear-induced fainting in healthy individuals The paleolithic-threat hypothesis
The Paleolithic-Threat
hypothesis reviewed here posits
that habitual efferent fainting can
be traced back to fear-induced
allelic polymorphisms that were
selected into some genomes of
anatomically, mitochondrially, and
neurally modern humans (Homo
sapiens sapiens) in the Mid-Paleolithic because of the survival
advantage they conferred during
periods of inescapable threat. We
posit that during Mid-Paleolithic
warfare an encounter with “a
stranger holding a sharp object”
was consistently associated with
threat to life. A heritable hard-
wired or firm-wired (prepotentiated) predisposition to abruptly
increase vagal tone and collapse
flaccidly rather than freeze or
attempt to flee or fight in response
to an approaching sharp object, a
minor injury, or the sight of blood,
polymorphism for the hemodynamically “paradoxical” flaccid-
immobility in response to these
stimuli may have increased some
non-combatants’ chances of survival. This is consistent with the
unusual age and sex pattern of
fear-induced fainting. The Paleolithic-Threat hypothesis also predicts a link to various hypo-androgenic states (e.g. low dehydroxyepiandrosterone-sulfate. We offer
five predictions testable via epidemiological, clinical, and ethological/primatological methods. The
Paleolithic-Threat hypothesis has
implications for research in the
aftermath of man-made disasters,
such as terrorism against civilians,
a traumatic event in which this
hypothesis predicts epidemics of
fear-induced faintin
Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite(LaPr)SrMnO
We report a significant decrease in the low-temperature resistance induced by
the application of an electric current on the -plane in the paramagnetic
insulating (PMI) state of
(LaPr)SrMnO. A colossal
electroresistance effect attaining -95% is observed at lower temperatures. A
colossal magnetoresistive step appears near 5T at low temperatures below 10K,
accompanied by an ultrasharp width of the insulator-metal transition. Injection
of higher currents to the crystal causes a disappearance of the steplike
transition. These findings have a close relationship with the presence of the
short-range charge-ordered clusters pinned within the PMI matrix of the crystal
studied.Comment: 4 pages 3 figure
Anomalous pressure effect on the remanent lattice striction of a (La,Pr)SrMnO bilayered manganite single crystal
We have studied the pressure effect on magnetostriction, both in the
-plane and along the c-axis, of a (La,Pr)SrMnO
bilayered manganite single crystal over the temperature region where the
field-induced ferromagnetic metal (FMM) transition takes place. For comparison,
we have also examined the pressure dependence of magnetization curves at the
corresponding temperatures. The applied pressure reduces the critical field of
the FMM transition and it enhances the remanent magnetostriction. An anomalous
pressure effect on the remanent lattice relaxation is observed and is similar
to the pressure effect on the remanent magnetization along the c-axis. These
findings are understood from the view point that the double-exchange
interaction driven FMM state is strengthened by application of pressure.Comment: 7 pages,7 figure
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