16,366 research outputs found
Coulomb Drag as a Probe of Coupled Plasmon Modes in Parallel Quantum Wells
We show theoretically that the Coulomb drag rate between two parallel
quasi-two-dimensional electron gases is substantially enhanced by the coupled
acoustic and optic plasmon modes of the system at temperatures (where is the Fermi temperature) for experimentally relevant
parameters. The acoustic mode causes a sharp upturn in the scaled drag rate as
a function of temperature at . Other experimental signatures
of plasmon-dominated drag are a dependence on the well separation ,
and a peak in the drag rate as a function of relative carrier densities at
matched Fermi velocities.Comment: 10 pages, RevTeX 3.0, MIC-TH-
Plasmon enhancement of Coulomb drag in double quantum well systems
We derive an expression for the drag rate (i.e., interlayer momentum transfer
rate) for carriers in two coupled two-dimensional gases to lowest nonvanishing
order in the screened interlayer electron--electron interaction, valid for {\sl
arbitrary} intralayer scattering mechanisms, using the Boltzmann transport
equation. We calculate the drag rate for experimentally relevant parameters,
and show that for moderately high temperatures (, where
is the Fermi temperature) the dynamical screening of the interlayer results in
a large enhancement of the drag rate due to the presence of coupled plasmon
modes. This plasmon enhancement causes the scaled drag rate to have a peak (i)
as a function of temperature at , and (ii) as a function of
the ratio of densities of the carriers in the two layers when their Fermi
velocities are equal. We also show that the drag rate can be significantly
affected by the {\sl intralayer} scattering mechanisms; in particular, the drag
rate changes approximately by a factor of 2 when the dopant layer modulation
doped structures are moved in from 400~\AA to 100~\AA.Comment: RevTex, 21 pages, 7 postscript figure
Scheme for Attophysics Experiments at a X-ray SASE FEL
We propose a concept for production of high power coherent attosecond pulses
in X-ray range. An approach is based on generation of 8th harmonic of radiation
in a multistage HGHG FEL (high gain high harmonic free electron laser)
configuration starting from shot noise. Single-spike phenomena occurs when
electron bunch is passed through the sequence of four relatively short
undulators. The first stage is a conventional "long" wavelength (0.8 nm) SASE
FEL which operates in the high-gain linear regime. The 0.1 nm wavelength range
is reached by successive multiplication (0.8 nm 0.4 nm 0.2 nm
0.1 nm) in a stage sequence. Our study shows that the statistical properties of
the high-harmonic radiation from the SASE FEL, operating in linear regime, can
be used for selection of radiation pulses with a single spike in time domain.
The duration of the spikes is in attosecond range. Selection of single-spike
high-harmonic pulses is achieved by using a special trigger in data acquisition
system. The potential of X-ray SASE FEL at TESLA at DESY for generating
attosecond pulses is demonstrated. Since the design of XFEL laboratory at TESLA
is based on the use of long SASE undulators with tunable gap, no special place
nor additional FEL undulators are required for attophysics experiments. The use
of a 10 GW-level attosecond X-ray pulses at X-ray SASE FEL facility will enable
us to track processes inside atoms.Comment: 21 pages, 12 figures, submitted to Optics Communication
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