2,351 research outputs found
Complex wave function, Chiral spin order parameter and Phase Problem
We study the two dimensional Hubbard model by use of the ground state
algorithm in the Monte Carlo simulation. We employ complex wave functions as
trial function in order to have a close look at properties such as chiral spin
order (SO) and flux phase. For half filling, a particle-hole
transformation leads to sum rules with respect to the Green's functions for a
certain choice of a set of wave functions. It is then analytically shown that
the sum rules lead to the absence of the SO. Upon doping, we are
confronted with the sign problem, which in our case %ch appears as a ``phase
problem" due to the phase of the Monte Carlo weights. The average of the phase
shows an exponential decay as a function of inverse temperature similarly to
that of sign by Loh Jr. et. al. . We compare the numerical results with those
of exact numerical calculations.Comment: 28 pages, 9 figures(hard copy will be available upon request
Imaging phase separation near the Mott boundary in the correlated organic superconductors -(BEDT-TTF)X
Electronic phase separation consisting of the metallic and insulating domains
with 50 -- 100 m in diameter is found in the organic Mott system
-[(8-BEDT-TTF)(8-BEDT-TTF)]Cu[N(CN)]Br
by means of scanning micro-region infrared spectroscopy using the synchrotron
radiation. The phase separation appears below the critical end temperature 35
-- 40 K of the first order Mott transition. The observation of the macroscopic
size of the domains indicates a different class of the intrinsic electronic
inhomogeneity from the nano-scale one reported in the inorganic Mott systems
such as High- copper and manganese oxides.Comment: 4 pages, 3 figure
Optical probe of carrier doping by X-ray irradiation in organic dimer Mott insulator -(BEDT-TTF)Cu[N(CN)Cl
We investigated the infrared optical spectra of an organic dimer Mott
insulator -(BEDT-TTF)Cu[N(CN)]Cl, which was irradiated with
X-rays. We observed that the irradiation caused a large spectral weight
transfer from the mid-infrared region, where interband transitions in the dimer
and Mott-Hubbard bands take place, to a Drude part in a low-energy region; this
caused the Mott gap to collapse. The increase of the Drude part indicates a
carrier doping into the Mott insulator due to irradiation defects. The strong
redistribution of the spectral weight demonstrates that the organic Mott
insulator is very close to the phase border of the bandwidth-controlled Mott
transition.Comment: 4 pages, 4 figure
Formation of Primordial Protostars
The evolution of collapsing metal free protostellar clouds is investigated
for various masses and initial conditions.
We perform hydrodynamical calculations for spherically symmetric clouds
taking account of radiative transfer of the molecular hydrogen lines and the
continuum, as well as of chemistry of the molecular hydrogen.
The collapse is found to proceed almost self-similarly like Larson-Penston
similarity solution.
In the course of the collapse, efficient three-body processes transform
atomic hydrogen in an inner region of \sim 1 M_{\sun} entirely into molecular
form.
However, hydrogen in the outer part remains totally atomic although there is
an intervening transitional layer of several solar masses, where hydrogen is in
partially molecular form.
No opaque transient core is formed although clouds become optically thick to
H collision-induced absorption continuum, since H dissociation
follows successively.
When the central part of the cloud reaches stellar densities (), a very small hydrostatic core (\sim
5 \times 10^{-3} M_{\sun}) is formed and subsequently grows in mass as the
ambient gas accretes onto it.
The mass accretion rate is estimated to be 3.7 \times 10^{-2} M_{\sun}
{\rm yr^{-1}} (M_{\ast}/M_{\sun})^{-0.37}, where is instantaneous
mass of the central core, by using a similarity solution which reproduces the
evolution of the cloud before the core formation.Comment: 20 pages, 5 Postscript figures, uses AAS LaTe
Mott transition and superconductivity in the strongly correlated organic superconductor -(BEDT-TTF)Cu[N(CN)Br
The magnetic field effect on the phase diagram of the organic Mott system
-(BEDT-TTF)Cu[N(CN)]Br in which the bandwidth was tuned by
the substitution of deuterated molecules was studied by means of the
resistivity measurements performed in magnetic fields. The lower critical point
of the first-order Mott transition, which ended on the upper critical field
-temperature plane of the superconductivity, was determined
experimentally in addition to the previously observed upper critical end point.
The lower critical end point moved to a lower temperature with the suppression
of in magnetic fields and the Mott transition recognized so far as
the -shaped curve reached 0 when in the end.Comment: 5 pages, 4 figure
Disorder Effect on the Vortex Pinning by the Cooling Process Control in the Organic Superconductor -(BEDT-TTF)Cu[N(CN)]Br
We investigate the influence of disorders in terminal ethylene groups of
BEDT-TTF molecules (ethylene-disorders) on the vortex pinning of the organic
superconductor -(BEDT-TTF)Cu[N(CN)]Br. Magnetization
measurements are performed under different cooling-processes. The second peak
in the magnetization hysteresis curve is observed for all samples studied, and
the hysteresis width of the magnetization becomes narrower by cooling faster.
In contradiction to the simple pinning effect of disorder, this result shows
the suppression of the vortex pinning force by introducing more
ethylene-disorders. The ethylene-disorder domain model is proposed for
explaining the observed result. In the case of the system containing a moderate
number of the ethylene-disorders, the disordered molecules form a domain
structure and it works as an effective pinning site. On the contrary, an excess
number of the ethylene-disorders may weaken the effect of the domain structure,
which results in the less effective pinning force on the vortices.Comment: 6 pages, 6 figure
From ballistic to Brownian vortex motion in complex oscillatory media
We show that the breaking of the rotation symmetry of spiral waves in
two-dimensional complex (period-doubled or chaotic) oscillatory media by
synchronization defect lines (SDL) is accompanied by an intrinsic drift of the
pattern. Single vortex motion changes from ballistic flights at a well-defined
angle from the SDL to Brownian-like diffusion when the turbulent character of
the medium increases. It gives rise, in non-turbulent multi-spiral regimes, to
a novel ``vortex liquid''.Comment: 5 pages, 4 figure
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