14 research outputs found
Nonlinear effects in E Jahn-Teller model: Variational approach with excited phonon states and mode correlations
Interplay of nonlinear and quantum effects in the ground state of the
E Jahn-Teller model was investigated by the {\it variational
approach and exact numerical simulations}. They result in the recognition of
(i) importance of the admixture of {\it the first excited state of the
displaced harmonic oscillator} of the symmetric phonon mode in the ground state
of the system in the selftrapping-dominated regime; (ii) existence of {\it the
region of localized -undisplaced oscillator states} in the
tunneling-dominated regime. The effect (i) occurs owing to significant decrease
of the ground state energy on account of the overlapping contribution of the
symmetric phonon mode between the states of the same parity. This contribution
considerably improves variational results especially in the
selftrapping-dominated regime. Close to the Ee limit, the nonlinear
effects of {\it two-mode correlations} turn to be effective due to the
rotational symmetry of this case. In the tunneling-dominated regime the phonon
wave functions behave like the strongly localized harmonic oscillator ground
state and the effect (i) looses its significance.Comment: 28 pages,6 figure
Spatial Structure of Spin Polarons in the t-J Model
The deformation of the quantum Neel state induced by a spin polaron is
analyzed in a slave fermion approach. Our method is based on the selfconsistent
Born approximation for Green's and the wave function for the quasiparticle. The
results of various spin-correlation functions relative to the position of the
moving hole are discussed and shown to agree with those available from small
cluster calculations. Antiferromagnetic correlations in the direct neighborhood
of the hole are reduced, but they remain antiferromagnetic even for J as small
as 0.1 t. These correlation functions exhibit dipolar distortions in the spin
structure, which sensitively depend on the momentum of the quasiparticle. Their
asymptotic decay with the distance from the hole is governed by power laws, yet
the spectral weight of the quasiparticles does not vanish.Comment: 12 pages, 2 postscipt files with figures; uses REVTeX, to be
published in Phys. Rev. B, Feb. 199
A self-consistent analytic treatment of two holes in the
The behavior of two holes in the t-J model is analyzed on
the infinite square lattice by an extension of the self-consistent Born approximation,
which has proved to be very accurate in the single-hole problem. The main ingredient of
our theory is the exact form of the eigenstates. Our results agree well with those of
previous numerical studies of the problem. The d-wave bound state is found to have the
lowest energy with a critical value , and there is no indication for
a crossover between the d-wave and the p-wave bound states