5,831 research outputs found
S(k) for Haldane Gap Antiferromagnets: Large-scale Numerical Results vs. Field Theory and Experiment
The structure function, S(k), for the s=1, Haldane gap antiferromagnetic
chain, is measured accurately using the recent density matrix renormalization
group method, with chain-length 100. Excellent agreement with the nonlinear
model prediction is obtained, both at where a single
magnon process dominates and at where a two magnon process
dominates. We repeat our calculation with crystal field anisotropy chosen to
model NENP, obtaining good agreement with both field theory predictions and
recent experiments. Correlation lengths, gaps and velocities are determined for
both polarizations.Comment: 11 pages, 3 postscript figures included, REVTEX 3.0, UBCTP-93-02
Isomorphisms between Quantum Group Covariant q-Oscillator Systems Defined for q and 1/q
It is shown that there exists an isomorphism between q-oscillator systems
covariant under and . By the isomorphism, the
defining relations of covariant q-oscillator system are
transmuted into those of . It is also shown that the similar
isomorphism exists for the system of q-oscillators covariant under the quantum
supergroup . Furthermore the cases of q-deformed Lie
(super)algebras constructed from covariant q-oscillator systems are considered.
The isomorphisms between q-deformed Lie (super)algebras can not obtained by the
direct generalization of the one for covariant q-oscillator systems.Comment: LaTeX 13pages, RCNP-07
Theory of Transport Properties in the p-wave Superconducting State of Sr2RuO4 - A Microscopic Determination of the Gap Structure -
We provide a detailed quantitative analysis of transport properties in the
p-wave superconducting state of Sr2RuO4. Specifically, we calculate ultrasound
attenuation rate and electronic thermal conductivity within the mean field
approximation. The impurity scattering of the quasi-particles are treated
within the self-consistent T-matrix approximation, and assumed to be in the
unitarity limit. The momentum dependence of the gap function is determined by
solving the Eliashberg equation for a three-band Hubbard model with the
realistic electronic structure of Sr2RuO4. On the basis of the microscopic
theory, we can naturally expect nodal structures along the c-axis on the
cylindrical Fermi surfaces, even if we assume the chiral pairing state (i.e.,
\Delta(k) \sim k_x \pm {\rm i} k_y). Consequently, we obtain the temperature
dependence of the transport coefficients in agreement with the experimental
results. We can clarify that actually the thermal excitations on the passively
superconducting bands contribute significantly to the thermal conductivity in a
wide temperature range, in contrast to the case of other physical quantities.Comment: 12 pages, 7 figures, submitted to J. Phys. Soc. Jp
Edge spin accumulation in semiconductor two-dimensional hole gases
The controlled generation of localized spin densities is a key enabler of
semiconductor spintronics In this work, we study spin Hall effect induced edge
spin accumulation in a two-dimensional hole gas with strong spin orbit
interactions. We argue that it is an intrinsic property, in the sense that it
is independent of the strength of disorder scattering. We show numerically that
the spin polarization near the edge induced by this mechanism can be large, and
that it becomes larger and more strongly localized as the spin-orbit coupling
strength increases, and is independent of the width of the conducting strip
once this exceeds the elastic scattering mean-free-path. Our experiments in
two-dimensional hole gas microdevices confirm this remarkable spin Hall effect
phenomenology. Achieving comparable levels of spin polarization by external
magnetic fields would require laboratory equipment whose physical dimensions
and operating electrical currents are million times larger than those of our
spin Hall effect devices.Comment: 6 pages, 5 figure
Spin dynamics of the S=1/2 antiferromagnetic zig-zag ladder with anisotropy
We use exact diagonalization and the modified Lanczos method to study the
finite energy and finite momentum spectral weight of the longitudinal and
transverse spin excitations of the anisotropic zig-zag ladder. We find that the
spin excitations form continua of gapless or gapped spinons in the different
regions of the phase diagram. The results obtained are consistent with a
picture previously proposed that in the anisotropic case there is a transition
from a gapped regime to a gapless regime, for small interchain coupling. In
this regime we find a sharp low-energy peak in the structure function for the
transverse spin excitations, consistent with a finite stiffness.Comment: 17 figure
Breakdown of the Luttinger sum-rule at the Mott-Hubbard transition in the one-dimensional t1-t2 Hubbard model
We investigate the momentum distribution function near the Mott-Hubbard
transition in the one-dimensional t1-t2 Hubbard model (the zig-zag Hubbard
chain), with the density-matrix renormalization-group technique. We show that
for strong interactions the Mott-Hubbard transition occurs between the
metallic-phase and an insulating dimerized phase with incommensurate spin
excitations, suggesting a decoupling of magnetic and charge excitations not
present in weak coupling. We illustrate the signatures for the Mott-Hubbard
transition and the commensurate-incommensurate transition in the insulating
spin-gapped state in their respective ground-state momentum distribution
functions
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