47,349 research outputs found
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
Fermi surface evolution in the antiferromagnetic state for the electron-doped t-t'-t''-J model
By use of the slave-boson mean-field approach, we have studied the
electron-doped t-t'-t''-J model in the antiferromagnetic (AF) state. It is
found that at low doping the Fermi surface (FS) pockets appear around
and , and upon increasing doping the other ones will
form around . The evolution of the FS with
doping as well as the calculated spectral weight are consistent with the
experimental results.Comment: Fig. 4 is updated, to appear in Phys. Rev.
Theory of antiferromagnetism in the electron-doped cuprate superconductors
On the basis of the Hubbard model, we present the formulation of
antiferromagnetism in electron-doped cuprates using the fluctuation-exchange
approach. Taking into account the spin fluctuations in combination with the
impurity scattering effect due to the randomly distributed dopant-atoms, we
investigate the magnetic properties of the system. It is shown that the
antiferromagnetic transition temperature, the onset temperature of the
pseudogap formation, the single particle spectral density, and the staggered
magnetization obtained by the present approach are in very good agreement with
the experimental results. The distribution function in momentum space at very
low temperature is observed to differ significantly from that of the Fermi
liquid. Also, we find zero-energy peak in the density of states (DOS) of the
antiferromagnetic phase. This DOS peak is sharp in the low doping regime, and
disappears near the optimal doping where the AF order becomes weak.Comment: 12 pages, 19 figure
Reconstruction from Radon projections and orthogonal expansion on a ball
The relation between Radon transform and orthogonal expansions of a function
on the unit ball in \RR^d is exploited. A compact formula for the partial
sums of the expansion is given in terms of the Radon transform, which leads to
algorithms for image reconstruction from Radon data. The relation between
orthogonal expansion and the singular value decomposition of the Radon
transform is also exploited.Comment: 15 page
Single top production in the -channel at LHC: a realistic test of electroweak models
We compute the complete electroweak one-loop effect on the process of
-channel single top production at LHC in the Standard Model and in the MSSM
within the mSUGRA symmetry breaking scheme. We find that the one-loop
electroweak SM effect is large, and decreases the cross section of an amount
that is of the same size as that of the NLO QCD one. The genuine SUSY effect in
the mSUGRA scheme, for a general choice of benchmark points, is rather small.
It might become large and visible in more general scenarios around thresholds
involving light stop and neutralino mass values.Comment: 28 pages, 10 eps figure
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