9,982 research outputs found
Charge carrier correlation in the electron-doped t-J model
We study the t-t'-t''-J model with parameters chosen to model an
electron-doped high temperature superconductor. The model with one, two and
four charge carriers is solved on a 32-site lattice using exact
diagonalization. Our results demonstrate that at doping levels up to x=0.125
the model possesses robust antiferromagnetic correlation. When doped with one
charge carrier, the ground state has momenta (\pm\pi,0) and (0,\pm\pi). On
further doping, charge carriers are unbound and the momentum distribution
function can be constructed from that of the single-carrier ground state. The
Fermi surface resembles that of small pockets at single charge carrier ground
state momenta, which is the expected result in a lightly doped antiferromagnet.
This feature persists upon doping up to the largest doping level we achieved.
We therefore do not observe the Fermi surface changing shape at doping levels
up to 0.125
Hole correlation and antiferromagnetic order in the t-J model
We study the t-J model with four holes on a 32-site square lattice using
exact diagonalization. This system corresponds to doping level x=1/8. At the
``realistic'' parameter J/t=0.3, holes in the ground state of this system are
unbound. They have short range repulsion due to lowering of kinetic energy.
There is no antiferromagnetic spin order and the electron momentum distribution
function resembles hole pockets. Furthermore, we show evidence that in case
antiferromagnetic order exists, holes form d-wave bound pairs and there is
mutual repulsion among hole pairs. This presumably will occur at low doping
level. This scenario is compatible with a checkerboard-type charge density
state proposed to explain the ``1/8 anomaly'' in the LSCO family, except that
it is the ground state only when the system possesses strong antiferromagnetic
order
Continuous-time Diffusion Monte Carlo and the Quantum Dimer Model
A continuous-time formulation of the Diffusion Monte Carlo method for lattice
models is presented. In its simplest version, without the explicit use of trial
wavefunctions for importance sampling, the method is an excellent tool for
investigating quantum lattice models in parameter regions close to generalized
Rokhsar-Kivelson points. This is illustrated by showing results for the quantum
dimer model on both triangular and square lattices. The potential energy of two
test monomers as a function of their separation is computed at zero
temperature. The existence of deconfined monomers in the triangular lattice is
confirmed. The method allows also the study of dynamic monomers. A finite
fraction of dynamic monomers is found to destroy the confined phase on the
square lattice when the hopping parameter increases beyond a finite critical
value. The phase boundary between the monomer confined and deconfined phases is
obtained.Comment: 4 pages, 4 figures, revtex; Added a figure showing the
confinement/deconfinement phase boundary for the doped quantum dimer mode
Quantum phase transition induced by Dzyaloshinskii-Moriya in the kagome antiferromagnet
We argue that the S=1/2 kagome antiferromagnet undergoes a quantum phase
transition when the Dzyaloshinskii-Moriya coupling is increased. For
the system is in a moment-free phase and for the system develops
antiferromagnetic long-range order. The quantum critical point is found to be
using exact diagonalizations and finite-size scaling. This
suggests that the kagome compound ZnCu_6_3$ may be in a quantum
critical region controlled by this fixed point.Comment: 5 pages, 4 figures; v2: add. data included, show that D=0.1J is at a
quantum critical poin
- …