73 research outputs found
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
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
Comment on "T-dependence of the magnetic penetration depth in unconventional superconductors at low temperatures: Can it be linear?"
We show that the clean superconductor with line of gap nodes is not in
conflict with the Nernst theorem. The answer to the question in the title of
the Schopohl-Dolgov paper in Phys. Rev. Lett. 80 (1998) 4761 (cond-mat/9802264)
is yes.Comment: Comment to the paper by Schopohl and Dolgov in Phys. Rev. Lett. 80
(1998) 4761 (cond-mat/9802264), RevTex file, 1 page, no figures, typos are
corrected, submitted to Phys. Rev. Let
Theory of Optical Orientation in n-Type Semiconductors
Time resolved measurements of magnetization in n-GaAs have revealed a rich
array of spin decoherence processes, and have shown that fairly long lifetimes
(\sim 100 ns) can be achieved under certain circumstances. In time-resolved
Faraday rotation and time-resolved Kerr rotation the evolution of the
magnetization can be followed as a function of temperature, applied field,
doping level and excitation level. We present a theory for the spin relaxation
in n-GaAs based on a set of rate equations for two interacting thermalized
subsystems of spins: localized states on donor sites and itinerant states in
the conduction band. The conduction band spins relax by scattering from defects
or phonons through the D'yakonov-Perel' mechanism, while the localized spins
relax by interacting with phonons (when in an applied field) or through the
Dzyaloshinskii-Moriya interaction. In this model, numerous features of the
data, including puzzling temperature and doping dependences of the relaxation
time, find an explanation.Comment: 4 pages, 2 figures; revised version has a more complete discussion of
the Elliott-Yafet and spin-phonon decay mechanism
Superconductivity in the Two-Dimensional - Model at Low Hole Doping
By combining a generalized Lanczos scheme with the variational Monte Carlo
method we can optimize the short- and long-range properties of the groundstate
separately. This allows us to measure the long-range order of the groundstate
of the - model as a function of the coupling constant , and identify
a region of finite d-wave superconducting long-range order. With a lattice size
of 50 sites we can reliably examine hole densities down to 0.16.Comment: 12 pages and 4 PostScript figures, ReVTeX 3.0, ETH-TH/94-1
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