12 research outputs found
Ground-State Phase Diagram of the 1D t-J model
We examine the ground-state phase diagram of the t-J model in one dimension
by means of the Density Matrix Renormalization Group. This model is
characterized by a rich phase diagram as a function of the exchange interaction
J and the density n, displaying Luttinger-liquid (LL) behavior both of
repulsive and attractive (i.e. superconducting) nature, a spin-gap phase, and
phase-separation. The phase boundaries separating the repulsive from the
attractive LL phase as J is increased, and also the boundaries of the spin-gap
region at low densities, and phase-separation at even larger J, are determined
on the basis of correlation functions and energy-gaps. In particular, we shed
light on a contradiction between variational and renormalization-group (RG)
results about the extent of the spin-gap phase, that results larger than the
variational but smaller than the RG one. Furthermore, we show that the spin gap
can reach a sizable value (~ 0.1 t) at low enough filling, such that preformed
pairs should be observable at temperatures below these energy scales. No
evidence for a phase with clustering of more than two particles is found on
approaching phase separation.Comment: 14 page
Variational Study of the Spin-Gap Phase of the One-Dimensional t-J Model
We propose a correlated spin-singlet-pairs wave function to describe the
spin-gap phase of the one-dimensional model at low density. Adding a
Jastrow factor with a variational parameter, , first introduced by
Hellberg and Mele, is shown to correctly describe the long-range behavior
expected for the Luther-Emery phase. Using the variational Monte Carlo method
we establish a relation between and the Luttinger exponent ,
.Comment: 4 pages (LaTex), 3 figures attache
Renormalization group analysis of the spin-gap phase in the one-dimensional t-J model
We study the spin-gap phase in the one-dimensional t-J model, assuming that
it is caused by the backward scattering process. Based on the renormalization
group analysis and symmetry, we can determine the transition point between the
Tomonaga-Luttinger liquid and the spin-gap phases, by the level crossing of the
singlet and the triplet excitations. In contrast to the previous works, the
obtained spin-gap region is unexpectedly large.
We also check that the universality class of the transition belongs to the
SU(2) Wess-Zumino-Witten model.Comment: 4 pages(RevTeX), 5 figures(EPS), TITCMT-97-10, to appear in Phys.
Rev. Let
On the Liaison Between Superconductivity and Phase Separation
Models of strongly correlated electrons that tend to phase separate are
studied including a long-range 1/r repulsive interaction. It is observed that
charge-density-wave states become stable as the strength of the 1/r term, , is increased. Due to this effect, the domain of stability of the
superconducting phases that appear near phase separation at is not enlarged by a 1/r interaction as naively expected. Nevertheless,
superconductivity exists in a wide region of parameter space, even if phase
separation is suppressed. Our results have implications for some theories of
the cuprates.Comment: 11 pages, 9 postscript figures are appende
Variational state based on the Bethe ansatz solution and a correlated singlet liquid state in the one-dimensional t-J model
The one-dimensional t-J model is investigated by the variational Monte Carlo
method. A variational wave function based on the Bethe ansatz solution is newly
proposed, where the spin-charge separation is realized, and a long-range
correlation factor of Jastrow-type is included. In most regions of the phase
diagram, this wave function provides an excellent description of the
ground-state properties characterized as a Tomonaga-Luttinger liquid; Both of
the amplitude and exponent of correlation functions are correctly reproduced.
For the spin-gap phase, another trial state of correlated singlet pairs with a
Jastrow factor is introduced. This wave function shows generalized Luther-Emery
liquid behavior, exhibiting enhanced superconducting correlations and
exponential decay of the spin correlation function. Using these two variational
wave functions, the whole phase diagram is determined. In addition, relations
between the correlation exponent and variational parameters in the trial
functions are derived.Comment: REVTeX 3.0, 27 pages. 7 figures available upon request
([email protected]). To be published in Phys. Rev. B 5
Coupling to optical phonons in the one-dimensional t-J model: Effects on superconducting fluctuations and phase separation
The one-dimensional (1D) - Holstein model is studied by exact
diagonalization of finite rings using a variational approximation for the
phonon states. Due to renormalization effects induced by the phonons, for
intermediate electron-phonon coupling, the phase separation (PS) boundary, and
with it the region of dominating superconducting fluctuations is shifted
substantially to smaller values of as compared to the pure - model.
Superconducting correlations are weakened through charge density wave
interactions mediated by the phonons. Possible consequences for the high
oxides are discussed.Comment: 4 pages, Latex2
Mean-field renormalization group theory of the t-J model
Ankara : The Department of Physics and the Institute of Engineering and Science of Bilkent University, 2002.Thesis (Master's) -- Bilkent University, 2002.Includes bibliographical references leaves 54.The quantum nature of the high temperature superconductivity models makes
analytical approaches to these systems almost impossible to implement. In this
thesis, a computational study of the one and two dimensional t − J models that
combines mean-field treatments with renormalization group techniques will be
presented. This allows one to deal with the noncommutations of the operators
at two consecutive sites of the lattices on which these models are defined. The
resulting phase diagram for the 1D t − J model reveals an antiferromagnetic
ground state, which may, upon doping with increasing temperature, show striped
formation that is seen in the high-Tc cuprates. The qualitative features of the
phase diagram of the 2D case is also presented, which reveals a phase transition
between the disordered and antiferomagnetically ordered phases.Şen, CengizM.S