10,049 research outputs found
BCS-BEC crossover in nuclear matter with the relativistic Hartree-Bogoliubov theory
Based on the relativistic Hartree-Bogoliubov theory, the influence of the
pairing interaction strength on the di-neutron correlations and the crossover
from superfluidity of neutron Cooper pairs in the channel to
Bose-Einstein condensation of di-neutron pairs is systematically investigated
in the nuclear matter. The bare nucleon-nucleon interaction Bonn-B is taken in
the particle-particle channel with an effective factor to simulate the medium
effects and take into account the possible ambiguity of pairing force, and the
effective interaction PK1 is used in the particle-hole channel. If the
effective factor is larger than 1.10, a di-neutron BEC state appears in the
low-density limit, and if it is smaller than 0.85, the neutron Cooper pairs are
found totally in the weak coupling BCS region. The reference values of several
characteristic quantities which characterize the BCS-BEC crossover are obtained
respectively from the dimensionless parameter with the
scattering length and the neutron Fermi momentum, the
zero-momentum transfer density correlation function D(0) and the effective
chemical potential .Comment: 8 pages, 4 figures, 2 tables, Accepted Thursday Jun 14, 2012 for
Physical Review
Searching Signals in Chinese Ancient Records for the C Increases in AD 774-775 and in AD 992-993
According to the analysis of the C content of two Japanese trees over
a period of approximately 3000 years at high time resolution, Miyake (2012)
found a rapid increase at AD 774-775 and later on at AD 992-993 (Miyake 2013).
This corresponds to a high-energy event happened within one year that input
-ray energy about 710erg to the Earth, leaving the
origin a mystery. Such strong event should have an unusual optical counterpart,
and have been recorded in historical literature. We searched Chinese historical
materials around AD 744-775 and AD 992-993, but no remarkable event was found
except a violent thunderstorm in AD 775. However, the possibility of a
thunderstorm containing so much energy is still unlikely. We conclude the event
caused the C increase is still unclear. This event most probably has no
optical counterpart, and short gamma-ray burst, giant flare of a soft gamma-ray
repeater and terrestrial -ray flash may all be the candidates.Comment: 8 pages, 3 figure
Doping dependence of the electron-doped cuprate superconductors from the antiferromagnetic properties of the Hubbard model
Within the Kotliar-Ruckenstein slave-boson approach, we have studied the
antiferromagnetic (AF) properties for the --- model applied to
electron-doped cuprate superconductors. Due to inclusion of spin fluctuations
the AF order decreases with doping much faster than obtained in the
Hartree-Fock theory. Under an intermediate {\it constant} the calculated
doping evolution of the spectral intensity has satisfactorily reproduced the
experimental results, without need of a strongly doping-dependent as argued
earlier. This may reconcile a discrepancy suggested in recent studies on
photoemission and optical conductivity.Comment: 5 pages, 4 eps figures, minor improvement, references added, to
appear in Phys. Rev.
Study of gossamer superconductivity and antiferromagnetism in the t-J-U model
The d-wave superconductivity (dSC) and antiferromagnetism are analytically
studied in a renormalized mean field theory for a two dimensional t-J model
plus an on-site repulsive Hubbard interaction . The purpose of introducing
the term is to partially impose the no double occupancy constraint by
employing the Gutzwiller approximation. The phase diagrams as functions of
doping and are studied. Using the standard value of and
in the large limit, we show that the antiferromagnetic (AF) order emerges
and coexists with the dSC in the underdoped region below the doping
. The dSC order parameter increases from zero as the doping
increases and reaches a maximum near the optimal doping . In
the small limit, only the dSC order survives while the AF order disappears.
As increased to a critical value, the AF order shows up and coexists with
the dSC in the underdoped regime. At half filing, the system is in the dSC
state for small and becomes an AF insulator for large . Within the
present mean field approach, We show that the ground state energy of the
coexistent state is always lower than that of the pure dSC state.Comment: 7 pages, 8 figure
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