682 research outputs found
Spin exchange in quantum rings and wires in the Wigner-crystal limit
We present a controlled method for computing the exchange coupling in
strongly correlated one-dimensional electron systems. It is based on the
asymptotically exact relation between the exchange constant and the
pair-correlation function of spinless electrons. Explicit results are obtained
for thin quantum rings with realistic Coulomb interactions, by calculating this
function via a many-body instanton approach.Comment: 7 pages, 2 figures. Changes in the text and figures to improve
readability; added reference
Solitonic Excitations in Linearly Coherent Channels of Bilayer Quantum Hall Stripes
In some range of interlayer distances, the ground state of the
two-dimensional electron gas at filling factor nu =4N+1 with N=0,1,2,... is a
coherent stripe phase in the Hartree-Fock approximation. This phase has
one-dimensional coherent channels that support charged excitations in the form
of pseudospin solitons. In this work, we compute the transport gap of the
coherent striped phase due to the creation of soliton-antisoliton pairs using a
supercell microscopic unrestricted Hartree-Fock approach. We study this gap as
a function of interlayer distance and tunneling amplitude. Our calculations
confirm that the soliton-antisoliton excitation energy is lower than the
corresponding Hartree-Fock electron-hole pair energy. We compare our results
with estimates of the transport gap obtained from a field-theoretic model valid
in the limit of slowly varying pseudospin textures.Comment: 15 pages, 8 figure
Cyclotron resonance in a two-dimensional electron gas with long-range randomness
We show that the the cyclotron resonance in a two-dimensional electron gas
has non-trivial properties if the correlation length of the disorder is larger
than the de Broglie wavelength: (a) the lineshape assumes three different forms
in strong, intermediate, and weak magnetic fields (b) at the transition from
the intermediate to the weak fields the linewidth suddenly collapses due to an
explosive growth in the fraction of electrons with a diffusive-type dynamics.Comment: A few typos correcte
Ground state phase diagram of 2D electrons in a high Landau level: - DMRG study
The ground state phase diagram of 2D electrons in a high Landau level (index
N=2) is studied by the density matrix renormalization group method. Pair
correlation functions are systematically calculated for various filling factors
from v=1/8 to 1/2. It is shown that the ground state phase diagram consists of
three different CDW states called stripe-phase, bubble-phase, and Wigner
crystal. The boundary between the stripe and the bubble phases is determined to
be v_c = 0.38, and that for the bubble phase and Wigner crystal is v_c = 0.24.
Each transition is of first order.Comment: 4 pages, 6 figure
Local Geometry of the Fermi Surface and Magnetoacoustic Responce of Two-Dimensional Electron Systems in Strong Magnetic Fields
A semiclassical theory for magnetotrasport in a quantum Hall system near
filling factor based on the Composite Fermions physical picture is
used to analyze the effect of local flattening of the Composite Fermion Fermi
surface (CF-FS) upon magnetoacoustic oscllations. We report on calculations of
the velocity shift and attenuation of a surface acoustic wave (SAW) which
travels above the two-dimensional electron system, and we show that local
geometry of the CF-FS could give rise to noticeable changes in the magnitude
and phase of the oscillations. We predict these changes to be revealed in
experiments, and to be used in further studies of the shape and symmetries of
the CF-FS. Main conclusions reported here could be applied to analyze
magnetotransport in quantum Hall systems at higher filling factors provided the Fermi-liquid-like state of the system.Comment: 7 pages, 2 figure
Skyrme and Wigner crystals in graphene
At low-energy, the band structure of graphene can be approximated by two
degenerate valleys about which the electronic spectra of the
valence and conduction bands have linear dispersion relations. An electronic
state in this band spectrum is a linear superposition of states from the
and sublattices of the honeycomb lattice of graphene. In a quantizing
magnetic field, the band spectrum is split into Landau levels with level N=0
having zero weight on the sublattice for the valley.
Treating the valley index as a pseudospin and assuming the real spins to be
fully polarized, we compute the energy of Wigner and Skyrme crystals in the
Hartree-Fock approximation. We show that Skyrme crystals have lower energy than
Wigner crystals \textit{i.e.} crystals with no pseudospin texture in some range
of filling factor around integer fillings. The collective mode spectrum
of the valley-skyrmion crystal has three linearly-dispersing Goldstone modes in
addition to the usual phonon mode while a Wigner crystal has only one extra
Goldstone mode with a quadratic dispersion. We comment on how these modes
should be affected by disorder and how, in principle, a microwave absorption
experiment could distinguish between Wigner and Skyrme crystals.Comment: 14 pages with 11 figure
A model of large volumetric capacitance in graphene supercapacitors based on ion clustering
Electric double layer supercapacitors are promising devices for high-power
energy storage based on the reversible absorption of ions into porous,
conducting electrodes. Graphene is a particularly good candidate for the
electrode material in supercapacitors due to its high conductivity and large
surface area. In this paper we consider supercapacitor electrodes made from a
stack of graphene sheets with randomly-inserted "spacer" molecules. We show
that the large volumetric capacitances C > 100 F/cm^3 observed experimentally
can be understood as a result of collective intercalation of ions into the
graphene stack and the accompanying nonlinear screening by graphene electrons
that renormalizes the charge of the ion clusters.Comment: 13 pages, 5 figures; additional discussion and supporting
calculations adde
Ground-state energy of the electron liquid in ultrathin wires
The ground-state energy and the density correlation function of the electron
liquid in a thin one-dimensional wire are computed. The calculation is based on
an approximate mapping of the problem with a realistic Coulomb interaction law
onto exactly solvable models of mathematical physics. This approach becomes
asymptotically exact in the limit of small wire radius but remains numerically
accurate even for modestly thin wires.Comment: (v3) Replaced with the published version. 4 pages, 1 figur
Orientation of the Stripe Formed by the Two-Dimensional Electrons in Higher Landau Levels
Effect of periodic potential on the stripe phase realized in the higher
Landau levels is investigated by the Hartree-Fock approximation. The period of
the potential is chosen to be two to six times of the fundamental period of the
stripe phase. It is found that the stripe aligns perpendicularly to the
external potential in contrast to a naive expectation and hydrodynamic theory.
Charge modulation towards the Wigner crystallization along the stripe is
essential for the present unexpected new result.Comment: 5 pages, RevTex, two figures included in the tex
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