2,339 research outputs found
Haldane Sashes in Quantum Hall Spectra
We show that the low-temperature sash features in the lowest Landau-level
(LLL) tunneling density-of-states (TDOS) recently discovered by Dial and
Ashoori are intimately related to the discrete Haldane-pseudopotential
interaction energy scales that govern fractional quantum Hall physics. Our
analysis is based on expressions for the tunneling density-of-states which
become exact at filling factors close to and , where the sash
structure is most prominent. We comment on other aspects of LLL correlation
physics that can be revealed by accurate temperature-dependent tunneling data.Comment: Added referenc
Dielectric function, screening, and plasmons in 2D graphene
The dynamical dielectric function of two dimensional graphene at arbitrary
wave vector and frequency , , is calculated in
the self-consistent field approximation. The results are used to find the
dispersion of the plasmon mode and the electrostatic screening of the Coulomb
interaction in 2D graphene layer within the random phase approximation. At long
wavelengths () the plasmon dispersion shows the local classical
behavior , but the density dependence of the
plasma frequency () is different from the usual 2D
electron system (). The wave vector dependent plasmon
dispersion and the static screening function show very different behavior than
the usual 2D case.Comment: 6 pages, 3 figure
Nonlinear photon transport in a semiconductor waveguide-cavity system containing a single quantum dot: Anharmonic cavity-QED regime
We present a semiconductor master equation technique to study the
input/output characteristics of coherent photon transport in a semiconductor
waveguide-cavity system containing a single quantum dot. We use this approach
to investigate the effects of photon propagation and anharmonic cavity-QED for
various dot-cavity interaction strengths, including weakly-coupled,
intermediately-coupled, and strongly-coupled regimes. We demonstrate that for
mean photon numbers much less than 0.1, the commonly adopted weak excitation
(single quantum) approximation breaks down, even in the weak coupling regime.
As a measure of the anharmonic multiphoton-correlations, we compute the Fano
factor and the correlation error associated with making a semiclassical
approximation. We also explore the role of electron--acoustic-phonon scattering
and find that phonon-mediated scattering plays a qualitatively important role
on the light propagation characteristics. As an application of the theory, we
simulate a conditional phase gate at a phonon bath temperature of K in the
strong coupling regime.Comment: To appear in PR
Non-Markovian disentanglement dynamics of two-qubit system
We investigated the disentanglement dynamics of two-qubit system in
Non-Markovian approach. We showed that only the couple strength with the
environment near to or less than fine-structure constant 1/137, entanglement
appear exponential decay for a certain class of two-qubit entangled state.
While the coupling between qubit and the environment is much larger, system
always appears the sudden-death of entanglement even in the vacuum environment.Comment: 17 pages, 3 figure
Phonon-induced dephasing of singlet-triplet superpositions in double quantum dots without spin-orbit coupling
We show that singlet-triplet superpositions of two-electron spin states in a
double quantum dot undergo a phonon-induced pure dephasing which relies only on
the tunnel coupling between the dots and on the Pauli exclusion principle. As
such, this dephasing process is independent of spin-orbit coupling or hyperfine
interactions. The physical mechanism behind the dephasing is elastic phonon
scattering, which persists to much lower temperatures than real phonon-induced
transitions. Quantitative calculations performed for a lateral GaAs/AlGaAs
gate-defined double quantum dot yield micro-second dephasing times at
sub-Kelvin temperatures, which is consistent with experimental observations.Comment: Extended versio
Many body effects in finite metallic carbon nanotubes
The non homogeneity of the charge distribution in a carbon nanotube leads to
the formation of an excitonic resonance, in a similar way to the one observed
in X-ray absorption in metals. As a result, a positive anomaly at low bias
appears in the tunnelling density of states. This effect depends on the
screening of the electron--electron interactions by metallic gates, and it
modifies the coupling of the nanotube to normal and superconducting electrodes.Comment: 5 page
Quench dynamics of correlated quantum dots
We study the relaxation dynamics of a quantum dot with local Coulomb
correlations coupled to two noninteracting leads which are held in
grandcanonical equilibrium. Only charge degrees of freedom are considered and
the dot is described by a model which in the scaling limit becomes equivalent
to the interacting resonant level model. The time evolution of the current and
dot occupancy resulting out of changes of the dot-lead coupling, the dots
onsite energy, or the charging energy are studied. Abrupt and smooth parameter
changes as well as setups with and without driving bias voltage are considered.
For biased dots we investigate the often studied response after turning on the
dot-lead coupling but also the experimentally more relevant case in which the
voltage is turned on. We identify and explain a variety of interesting
many-body effects and clarify the role of initial correlations.Comment: 8 pages, 10 figure
Analysis of transport properties of iron pnictides: spin-fluctuation scenario
We present a phenomenological theory of quasiparticle scattering and
transport relaxation in the normal state of iron pnictides based on the
simplified two-band model coupled via spin fluctuations. In analogy with
anomalous properties of cuprates it is shown that a large and anomalous
normal-state resistivity and thermopower can be interpreted as the consequence
of strong coupling to spin fluctuations. The generalization to the
superconducting phase is also discussed.Comment: Revised version, 6 pages, 11 references adde
Valley dependent many-body effects in 2D semiconductors
We calculate the valley degeneracy () dependence of the many-body
renormalization of quasiparticle properties in multivalley 2D semiconductor
structures due to the Coulomb interaction between the carriers. Quite
unexpectedly, the dependence of many-body effects is nontrivial and
non-generic, and depends qualitatively on the specific Fermi liquid property
under consideration. While the interacting 2D compressibility manifests
monotonically increasing many-body renormalization with increasing , the
2D spin susceptibility exhibits an interesting non-monotonic dependence
with the susceptibility increasing (decreasing) with for smaller (larger)
values of with the renormalization effect peaking around .
Our theoretical results provide a clear conceptual understanding of recent
valley-dependent 2D susceptibility measurements in AlAs quantum wells.Comment: 5 pages, 3 figure
Velocity renormalization and anomalous quasiparticle dispersion in extrinsic graphene
Using many-body diagrammatic perturbation theory we consider carrier density-
and substrate-dependent many-body renormalization of doped or gated graphene
induced by Coulombic electron-electron interaction effects. We quantitatively
calculate the many-body spectral function, the renormalized quasiparticle
energy dispersion, and the renormalized graphene velocity using the
leading-order self-energy in the dynamically screened Coulomb interaction
within the ring diagram approximation. We predict experimentally detectable
many-body signatures, which are enhanced as the carrier density and the
substrate dielectric constant are reduced, finding an intriguing instability in
the graphene excitation spectrum at low wave vectors where interaction
completely destroys all particle-like features of the noninteracting linear
dispersion. We also make experimentally relevant quantitative predictions about
the carrier density and wave-vector dependence of graphene velocity
renormalization induced by electron-electron interaction. We compare on-shell
and off-shell self-energy approximations within the ring diagram approximation,
finding a substantial quantitative difference between their predicted velocity
renormalization corrections in spite of the generally weak-coupling nature of
interaction in graphene.Comment: 9 pages, 6 figure
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