245 research outputs found
SU(4) Spin-Orbital Two-Leg Ladder, Square and Triangle Lattices
Based on the generalized valence bond picture, a Schwinger boson mean field
theory is applied to the symmetric SU(4) spin-orbital systems. For a two-leg
SU(4) ladder, the ground state is a spin-orbital liquid with a finite energy
gap, in good agreement with recent numerical calculations. In two-dimensional
square and triangle lattices, the SU(4) Schwinger bosons condense at
(\pi/2,\pi/2) and (\pi/3,\pi/3), respectively. Spin, orbital, and coupled
spin-orbital static susceptibilities become singular at the wave vectors, twice
of which the bose condensation arises at. It is also demonstrated that there
are spin, orbital, and coupled spin-orbital long-range orderings in the ground
state.Comment: 5 page
Tunneling ``zero-bias'' anomaly in the quasi-ballistic regime
For the first time, we study the tunneling density of states (DOS) of the
interacting electron gas beyond the diffusive limit. A strong correction to the
DOS persists even at electron energies exceeding the inverse transport
relaxation time, which could not be expected from the well-known
Altshuler-Aronov-Lee (AAL) theory. This correction originates from the
interference between the electron waves scattered by an impurity and by the
Friedel oscillation this impurity creates. Account for such processes also
revises the AAL formula for the DOS in the diffusive limit.Comment: 4 pages, 2 .eps figures, submitted to Phys. Rev. Let
Intrasubband and Intersubband Electron Relaxation in Semiconductor Quantum Wire Structures
We calculate the intersubband and intrasubband many-body inelastic Coulomb
scattering rates due to electron-electron interaction in two-subband
semiconductor quantum wire structures. We analyze our relaxation rates in terms
of contributions from inter- and intrasubband charge-density excitations
separately. We show that the intersubband (intrasubband) charge-density
excitations are primarily responsible for intersubband (intrasubband) inelastic
scattering. We identify the contributions to the inelastic scattering rate
coming from the emission of the single-particle and the collective excitations
individually. We obtain the lifetime of hot electrons injected in each subband
as a function of the total charge density in the wire.Comment: Submitted to PRB. 20 pages, Latex file, and 7 postscript files with
Figure
Coulomb scattering lifetime of a two-dimensional electron gas
Motivated by a recent tunneling experiment in a double quantum-well system,
which reports an anomalously enhanced electronic scattering rate in a clean
two-dimensional electron gas, we calculate the inelastic quasiparticle lifetime
due to electron-electron interaction in a single loop dynamically screened
Coulomb interaction within the random-phase-approximation. We obtain excellent
quantitative agreement with the inelastic scattering rates in the tunneling
experiment without any adjustable parameter, finding that the reported large
( a factor of six) disagreement between theory and experiment arises from
quantitative errors in the existing theoretical work and from the off-shell
energy dependence of the electron self-energy.Comment: 11 pages, RevTex, figures included. Also available at
http://www-cmg.physics.umd.edu/~lzheng
Synthesizing attractors of Hindmarsh-Rose neuronal systems
In this paper a periodic parameter switching scheme is applied to the
Hindmarsh-Rose neuronal system to synthesize certain attractors. Results show
numerically, via computer graphic simulations, that the obtained synthesized
attractor belongs to the class of all admissible attractors for the
Hindmarsh-Rose neuronal system and matches the averaged attractor obtained with
the control parameter replaced with the averaged switched parameter values.
This feature allows us to imagine that living beings are able to maintain vital
behavior while the control parameter switches so that their dynamical behavior
is suitable for the given environment.Comment: published in Nonlinear Dynamic
Electron-electron interactions and two-dimensional - two-dimensional tunneling
We derive and evaluate expressions for the dc tunneling conductance between
interacting two-dimensional electron systems at non-zero temperature. The
possibility of using the dependence of the tunneling conductance on voltage and
temperature to determine the temperature-dependent electron-electron scattering
rate at the Fermi energy is discussed. The finite electronic lifetime produced
by electron-electron interactions is calculated as a function of temperature
for quasiparticles near the Fermi circle. Vertex corrections to the random
phase approximation substantially increase the electronic scattering rate. Our
results are in an excellent quantitative agreement with experiment.Comment: Revtex style, 21 pages and 8 postscript figures in a separate file;
Phys. Rev. B (in press
Correlations, compressibility, and capacitance in double-quantum-well systems in the quantum Hall regime
In the quantum Hall regime, electronic correlations in double-layer
two-dimensional electron systems are strong because the kinetic energy is
quenched by Landau quantization. In this article we point out that these
correlations are reflected in the way the partitioning of charge between the
two-layers responds to a bias potential. We report on illustrative calculations
based on an unrestricted Hartree-Fock approximation which allows for
spontaneous inter-layer phase coherence. The possibility of studying
inter-layer correlations by capacitive coupling to separately contacted
two-dimensional layers is discussed in detail.Comment: RevTex style, 21 pages, 6 postscript figures in a separate file;
Phys. Rev. B (in press
Quantum Ferromagnetism and Phase Transitions in Double-Layer Quantum Hall Systems
Double layer quantum Hall systems have interesting properties associated with
interlayer correlations. At where is an odd integer they exhibit
spontaneous symmetry breaking equivalent to that of spin easy-plane
ferromagnets, with the layer degree of freedom playing the role of spin. We
explore the rich variety of quantum and finite temperature phase transitions in
these systems. In particular, we show that a magnetic field oriented parallel
to the layers induces a highly collective commensurate-incommensurate phase
transition in the magnetic order.Comment: 4 pages, REVTEX 3.0, IUCM93-013, 1 FIGURE, hardcopy available from:
[email protected]
Double-Layer Systems at Zero Magnetic Field
We investigate theoretically the effects of intralayer and interlayer
exchange in biased double-layer electron and hole systems, in the absence of a
magnetic field. We use a variational Hartree-Fock-like approximation to analyze
the effects of layer separation, layer density, tunneling, and applied gate
voltages on the layer densities and on interlayer phase coherence. In agreement
with earlier work, we find that for very small layer separations and low layer
densities, an interlayer-correlated ground state possessing spontaneous
interlayer coherence (SILC) is obtained, even in the absence of interlayer
tunneling. In contrast to earlier work, we find that as a function of total
density, there exist four, rather than three, distinct noncrystalline phases
for balanced double-layer systems without interlayer tunneling. The newly
identified phase exists for a narrow range of densities and has three
components and slightly unequal layer densities, with one layer being spin
polarized, and the other unpolarized. An additional two-component phase is also
possible in the presence of sufficiently strong bias or tunneling. The
lowest-density SILC phase is the fully spin- and pseudospin-polarized
``one-component'' phase discussed by Zheng {\it et al.} [Phys. Rev. B {\bf 55},
4506 (1997)]. We argue that this phase will produce a finite interlayer Coulomb
drag at zero temperature due to the SILC. We calculate the particle densities
in each layer as a function of the gate voltage and total particle density, and
find that interlayer exchange can reduce or prevent abrupt transfers of charge
between the two layers. We also calculate the effect of interlayer exchange on
the interlayer capacitance.Comment: 35 pages, 19 figures included. To appear in PR
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