134 research outputs found
Does the Two-Dimensional t-J Model have Hole Pockets?
We have calculated the high temperature series for the momentum distribution
function n_k of the 2D t-J model to 12th order in inverse temperature. By
extrapolating the series to T=0.2J we investigate the possibility of hole
pockets in the t-J model. We find no indication of hole pockets at an electron
density of n=0.9 with J/t=0.5 or J/t=1.0.Comment: 2 pages, 2 figures. Contribution to Spectroscopies of Novel
Superconductors 97, Cape Cod, M
Violation of Luttinger's Theorem in the Two-Dimensional t-J Model
We have calculated the high temperature series for the momentum distribution
function n_k of the 2D t-J model to 12th order in inverse temperature. By
extrapolating the series to T=0.2J we searched for a Fermi surface of the 2D
t-J model. We find that three criteria used for estimating the location of a
Fermi surface violate Luttinger's Theorem, implying the 2D t-J model does not
have an adiabatic connection to a non-interacting model.Comment: 4 pages, 5 figures. Version with grayscale figures available upon
reques
Theory of Electron Spin Relaxation in n-Doped Quantum Wells
Recent experiments have demonstrated long spin lifetimes in uniformly n-doped
quantum wells. The spin dynamics of exciton, localized, and conduction spins
are important for understanding these systems. We explain experimental behavior
by invoking spin exchange between all spin species. By doing so we explain
quantitatively and qualitatively the striking and unusual temperature
dependence in (110)-GaAs quantum wells. We discuss possible future experiments
to resolve the pertinent localized spin relaxation mechanisms. In addition, our
analysis allows us to propose possible experimental scenarios that will
optimize spin relaxation times in GaAs and CdTe quantum wells.Comment: Small corrections made. Accepted to Phys. Rev. B. 8 pages, 5 figure
Large physical spin approach for strongly correlated electrons
We present a novel approach for a systematic large--spin expansion of the
- Hamiltonian which enables us to work without the constraint of no
double occupancy. In our scheme we can perform the large--spin limit ensuring
that the low energy spin excitations are in {\em exact} correspondence with the
physical excitations of the Hilbert space. As a consequence, we
expect a smooth dependence of the physical quantities on the expansion
parameter . As a first application of the method we study the case of a
single hole in a N\'eel background. A systematic expansion in fluctuations
about this stable solution indicates that by increasing the quasiparticle
weight strongly depends on the momentum carried by the hole. Results, obtained
on small lattice sizes, are found in excellent agreement with exact
diagonalization data.Comment: RevTeX 3.0 + 2 postscript figures appended (search for FIG1a and
FIG1b ) revised, to appear in Phys. Lett.
Limits on Phase Separation for Two-Dimensional Strongly Correlated Electrons
From calculations of the high temperature series for the free energy of the
two-dimensional t-J model we construct series for ratios of the free energy per
hole. The ratios can be extrapolated very accurately to low temperatures and
used to investigate phase separation. Our results confirm that phase separation
occurs only for J/t greater than 1.2. Also, the phase transition into the phase
separated state has Tc of approximately 0.25J for large J/t.Comment: 4 pages, 6 figure
Phase diagram of the two-dimensional t--J model at low doping
The phase diagram of the planar t--J model at small hole doping is
investigated by finite size scaling of exact diagonalisation data of NXN
clusters (up to 26). Hole-droplet binding energies, compressibility and static
spin and charge correlations are calculated. Short range antiferromagnetic
correlations can produce attractive forces between holes leading to a very rich
phase diagram including a liquid of d-wave hole pairs (for ), a
liquid of hole droplets (quartets) for larger J/t ratios ()
and, at even larger coupling J/t, an instability towards phase separation.Comment: 3 pages, latex, 5 postscript figures, uuencode
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