173,914 research outputs found
Quasiclassical Green function in an external field and small-angle scattering
The quasiclassical Green functions of the Dirac and Klein-Gordon equations in
the external electric field are obtained with the first correction taken into
account. The relevant potential is assumed to be localized, while its spherical
symmetry is not required. Using these Green functions, the corresponding wave
functions are found in the approximation similar to the Furry-Sommerfeld-Maue
approximation. It is shown that the quasiclassical Green function does not
coincide with the Green function obtained in the eikonal approximation and has
a wider region of applicability. It is illustrated by the calculation of the
small-angle scattering amplitude for a charged particle and the forward photon
scattering amplitude. For charged particles, the first correction to the
scattering amplitude in the non-spherically symmetric potential is found. This
correction is proportional to the scattering angle. The real part of the
amplitude of forward photon scattering in a screened Coulomb potential is
obtained.Comment: 20 pages, latex, 1 figur
Relativistic Coulomb Green's function in -dimensions
Using the operator method, the Green's functions of the Dirac and
Klein-Gordon equations in the Coulomb potential are derived for
the arbitrary space dimensionality . Nonrelativistic and quasiclassical
asymptotics of these Green's functions are considered in detail.Comment: 9 page
Study of the triangular lattice tV model near x=1/3
We study extended Hubbard model on a triangular lattice near doping ,
which may be relevant for the recently discovered superconductor NaCoOHO. By generalizing this model to fermionic species, we
formulate a meanfield description in the limit of large . In meanfield, we
find two possible phases: a renormalized Fermi liquid and a \rt3rt3 charge
density wave state. The transition between the two phases is driven by
increasing the nearest neighbor repulsion and is found to be first order for
doping , but occurs close to the point of the local instability of the
uniform liquid. We also study fluctuations about the uniform meanfield state in
a systematic 1/N expansion, focusing on the residual interaction of
quasiparticles and possible superconducting instabilities due to this
interaction. Upon moving towards the CDW instability, the increasing charge
fluctuations favor a particular -wave triplet state. (This state was
recently discussed by Tanakaet al, cond-mat/0311266). We also report a direct
Gutzwiller wavefunction study of the spin-1/2 model.Comment: 9 pages, 5 figure
Electron-positron pair production in ion collisions at low velocity beyond Born approximation
We derive the spectrum and the total cross section of electromagnetic
pair production in the collisions of two nuclei at low relative
velocity . Both free-free and bound-free pair production is
considered. The parameters are assumed to be small
compared to unity but arbitrary compared to ( are the charge
numbers of the nuclei and is the fine structure constant). Due to a
suppression of the Born term by high power of , the first Coulomb
correction to the amplitude appears to be important at . The effect of a finite nuclear mass is discussed. In contrast to the
result obtained in the infinite nuclear mass limit, the terms
are not suppressed by the high power of and may easily dominate at
sufficiently small velocities.Comment: 9 pages, 1 figur
Susceptibility of a spinon Fermi surface coupled to a U(1) gauge field
We study the theory of a U(1) gauge field coupled to a spinon Fermi surface.
Recently this model has been proposed as a possible description of the organic
compound . We calculate the susceptibility of
this system and in particular examine the effect of pairing of the underlying
spin liquid. We show that this proposed theory is consistent with the observed
susceptibility measurements.Comment: 5 pages, 4 figure
Cuprates as doped U(1) spin liquids
We explore theoretically the notion that the underdoped cuprates may be
viewed as doped U(1) spin liquid Mott insulators. We pursue a conceptually
clear version of this idea that naturally incorporates several aspects of the
phenomenology of the cuprates. We argue that the low doping region may be
fruitfully discussed in terms of the universal physics associated with a
chemical potential tuned Mott transition between a U(1) spin liquid insulator
and a d-wave superconductor. A precise characterization of the deconfinement in
the U(1) spin liquid is provided by the emergence of a conserved gauge flux.
This extra conservation law should hold at least approximately in the
underdoped materials. Experiments that could possibly detect this conserved
gauge flux are proposed.Comment: 11 pages, 7 figure
- …