88 research outputs found
Checkerboard patterns in the t-J model
Using the density matrix renormalization group, we study the possibility of
real space checkerboard patterns arising as the ground states of the t-J model.
We find that checkerboards with a commensurate (pi,pi) background are not low
energy states and can only be stabilized with large external potentials.
However, we find that striped states with charge density waves along the
stripes can form approximate checkerboard patterns. These states can be
stabilized with a very weak external field aligning and pinning the CDWs on
different stripes.Comment: 4 pages, 5 figure
Cooper-pair transport through a Hubbard chain sandwiched between two superconductors: Density matrix renormalization group calculations
We present a numerical approach to study the coherent transport of Cooper
pairs through a Hubbard chain, and study the role of the contacts in achieving
perfect Andreev reflection. We calculate the pair transport using the Density
Matrix Renormalization Group by measuring the response of the system to quantum
pair fields with complex phases on the two ends of an open system. This
approach gives an effective superfluid weight which is in close agreement with
the Bethe Ansatz results for the superfluid weight for closed Hubbard rings.Comment: 5 pages, 6 figure
Effect of the W-term for a t-U-W Hubbard ladder
Antiferromagnetic and d_{x2-y2}-pairing correlations appear delicately
balanced in the 2D Hubbard model. Whether doping can tip the balance to pairing
is unclear and models with additional interaction terms have been studied. In
one of these, the square of a local hopping kinetic energy H_W was found to
favor pairing. However, such a term can be separated into a number of simpler
processes and one would like to know which of these terms are responsible for
enhancing the pairing. Here we analyze these processes for a 2-leg Hubbard
ladder
Competition Between Stripes and Pairing in a t-t'-J Model
As the number of legs n of an n-leg, t-J ladder increases, density matrix
renormalization group calculations have shown that the doped state tends to be
characterized by a static array of domain walls and that pairing correlations
are suppressed. Here we present results for a t-t'-J model in which a diagonal,
single particle, next-near-neighbor hopping t' is introduced. We find that this
can suppress the formation of stripes and, for t' positive, enhance the
d_{x^2-y^2}-like pairing correlations. The effect of t' > 0 is to cause the
stripes to evaporate into pairs and for t' < 0 to evaporate into
quasi-particles. Results for n=4 and 6-leg ladders are discussed.Comment: Four pages, four encapsulated figure
Probing the pairing symmetry and pair charge stiffness of doped ladders
We perform the numerical equivalent of a phase sensitive experiment on doped
ladders. We apply proximity effect fields with different complex phases
at both ends of an open system and we study the transport of Cooper pairs.
Measuring the response of the system and the induced Josephson current, Density
Matrix Renormalization Group calculations show how, depending on the doping
fraction, the rung-leg parity of the pair field changes from minus to plus as
the density of holes is increased. We also study the pair charge stiffness, and
we observe a supression of the superconductivity in the region where static
stripes appear. We compare our results with predictions from bosonization and
renormalization group analysis.Comment: 4 pages, 5 figure
Comment on ``Stripes and the t-J Model''
This is a comment being submitted to Physical Review Letters on a recent
letter by Hellberg and Manousakis on stripes in the t-J model.Comment: One reference correcte
Energetics of Domain Walls in the 2D t-J model
Using the density matrix renormalization group, we calculate the energy of a
domain wall in the 2D t-J model as a function of the linear hole density
\rho_\ell, as well as the interaction energy between walls, for J/t=0.35. Based
on these results, we conclude that the ground state always has domain walls for
dopings 0 < x < 0.3. For x < 0.125, the system has (1,0) domain walls with
\rho_\ell ~ 0.5, while for 0.125 < x < 0.17, the system has a possibly
phase-separated mixture of walls with \rho_\ell ~ 0.5 and \rho_\ell =1. For x >
0.17, there are only walls with \rho_\ell =1. For \rho_\ell = 1, diagonal (1,1)
domain walls have very nearly the same energy as (1,0) domain walls.Comment: Several minor changes. Four pages, four encapsulated figure
The Superconducting Condensation Energy and an Antiferromagnetic Exchange Based Pairing Mechanism
For the traditional low T_c superconductors, the superconducting condensation
energy is proportional to the change in energy of the ionic lattice between the
normal and superconducting state, providing a clear link between pairing and
the electron-ion interaction. Here, for the t-J model, we discuss an analogous
relationship between the superconducting condensation energy and the change in
the exchange energy between the normal and superconducting states. We point out
the possibility of measuring this using neutron scattering and note that such a
measurement, while certainly difficult, could provide important evidence for an
exchange interaction-based pairing mechanism.Comment: Replaced with revised versio
The Doped Two Chain Hubbard Model
The properties of the two-chain Hubbard Model doped away from half-filling
are investigated. The charge gap is found to vanish, but a finite spin gap
exists over a range of interchain hopping strength . In this range,
there are modified --like pairing correlations whose strength is
correlated with the size of the spin gap. It is found that the pair field
correlations are enhanced by the onsite Coulomb interaction U.Comment: 10 pages and 5 postscript figures, RevTeX 3.0, UCI-CMTHE-94-0
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