10,069 research outputs found
Exact Solution for Relativistic Two-Body Motion in Dilaton Gravity
We present an exact solution to the problem of the relativistic motion of 2
point masses in dimensional dilaton gravity. The motion of the bodies
is governed entirely by their mutual gravitational influence, and the spacetime
metric is likewise fully determined by their stress-energy. A Newtonian limit
exists, and there is a static gravitational potential. Our solution gives the
exact Hamiltonian to infinite order in the gravitational coupling constant.Comment: 6 pages, latex, 3 figure
Exact Charged 2-Body Motion and the Static Balance Condition in Lineal Gravity
We find an exact solution to the charged 2-body problem in
dimensional lineal gravity which provides the first example of a relativistic
system that generalizes the Majumdar-Papapetrou condition for static balance.Comment: latex,7 pages, 2 figure
A BCS-BEC crossover in the extended Falicov-Kimball model: Variational cluster approach
We study the spontaneous symmetry breaking of the excitonic insulator state
induced by the Coulomb interaction in the two-dimensional extended
Falicov-Kimball model. Using the variational cluster approximation (VCA) and
Hartree-Fock approximation (HFA), we evaluate the order parameter,
single-particle excitation gap, momentum distribution functions, coherence
length of excitons, and single-particle and anomalous excitation spectra, as a
function of at zero temperature. We find that in the weak-to-intermediate
coupling regime, the Fermi surface plays an essential role and calculated
results can be understood in close correspondence with the BCS theory, whereas
in the strong-coupling regime, the Fermi surface plays no role and results are
consistent with the picture of BEC. Moreover, we find that HFA works well both
in the weak- and strong-coupling regime, and that the difference between the
results of VCA and HFA mostly appears in the intermediate-coupling regime. The
reason for this is discussed from a viewpoint of the self-energy. We thereby
clarify the excitonic insulator state that typifies either a BCS condensate of
electron-hole pairs (weak-coupling regime) or a Bose-Einstein condensate of
preformed excitons (strong-coupling regime).Comment: 11 pages, 9 figure
Bogoliubov quasiparticle spectra of the effective d-wave model for cuprate superconductivity
An exact-diagonalization technique on finite-size clusters is used to study
the ground state and excitation spectra of the two-dimensional effective
fermion model, a fictious model of hole quasiparticles derived from numerical
studies of the two-dimensional t-J model at low doping. We show that there is
actually a reasonable range of parameter values where the -wave
pairing of holes occurs and the low-lying excitation can be described by the
picture of Bogoliubov quasiparticles in the BCS pairing theory. The gap
parameter of a size (where is the attractive
interaction between holes) is estimated at low doping levels. The paired state
gives way to the state of clustering of holes for some stronger attractions.Comment: 4 pages, RevTeX. Figures available upon request to
[email protected]. To be published in Phys. Rev.
Doping dependent quasiparticle band structure in cuprate superconductors
We present an exact diagonalization study of the single particle spectral
function in the so-called t-t'-t''-J model in 2D. As a key result, we find that
unlike the `pure' t-J model, hole doping leads to a major reconstruction of the
quasiparticle band structure near (pi,0): whereas for the undoped system the
quasiparticle states near (pi,0) are deep below the top of the band at
(pi/2,pi/2), hole doping shifts these states up to E_F, resulting in extended
flat band regions close to E_F and around (pi,0). This strong doping-induced
deformation can be directly compared to angle resolved photoemission results on
Sr_2 Cu Cl_2 O_2, underdoped Bi2212 and optimally doped Bi2212. We propose the
interplay of long range hopping and decreasing spin correlations as the
mechanism of this deformation.Comment: 4 pages, Revtex, with 4 embedded eps figures. Hardcopies of figures
(or the entire manuscript) can be obtained by e-mail request to
[email protected]
Theory of the waterfall phenomenon in cuprate superconductors
Based on exact diagonalization and variational cluster approximation
calculations we study the relationship between charge transfer models and the
corresponding single band Hubbard models. We present an explanation for the
waterfall phenomenon observed in angle resolved photoemission spectroscopy
(ARPES) on cuprate superconductors. The phenomenon is due to the destructive
interference between the phases of the O2p orbitals belonging to a given
Zhang-Rice singlet and the Bloch phases of the photohole which occurs in
certain regions of k-space. It therefore may be viewed as a direct experimental
visualisation of the Zhang-Rice construction of an effective single band model
for the CuO2 plane.Comment: 11 pages, 9 Postscript figure
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