10,108 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]
Self-energy and Fermi surface of the 2-dimensional Hubbard model
We present an exact diagonalization study of the self-energy of the
two-dimensional Hubbard model. To increase the range of available cluster sizes
we use a corrected t-J model to compute approximate Greens functions for the
Hubbard model. This allows to obtain spectra for clusters with 18 and 20 sites.
The self-energy has several `bands' of poles with strong dispersion and
extended incoherent continua with k-dependent intensity. We fit the self-energy
by a minimal model and use this to extrapolate the cluster results to the
infinite lattice. The resulting Fermi surface shows a transition from hole
pockets in the underdoped regime to a large Fermi surface in the overdoped
regime. We demonstrate that hole pockets can be completely consistent with the
Luttinger theorem. Introduction of next-nearest neighbor hopping changes the
self-energy stronlgy and the spectral function with nonvanishing
next-nearest-neighbor hopping in the underdoped region is in good agreement
with angle resolved photoelectron spectroscopy.Comment: 17 pages, 18 figure
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