135 research outputs found
Drift mobility of long-living excitons in coupled GaAs quantum wells
We observe high-mobility transport of indirect excitons in coupled GaAs
quantum wells. A voltage-tunable in-plane potential gradient is defined for
excitons by exploiting the quantum confined Stark effect in combination with a
lithographically designed resistive top gate. Excitonic photoluminescence
resolved in space, energy, and time provides insight into the in-plane drift
dynamics. Across several hundreds of microns an excitonic mobility of >10^5
cm2/eVs is observed for temperatures below 10 K. With increasing temperature
the excitonic mobility decreases due to exciton-phonon scattering.Comment: 3 pages, 3 figure
Theory of a two-level artificial molecule in laterally coupled quantum Hall droplets
We present a theory of laterally coupled quantum Hall droplets with electron
numbers (N1,N2) at filling factor . We show that the edge states of each
droplet are tunnel coupled and form a two-level artificial molecule. By
populating the edge states with one electron each a two electron molecule is
formed. We predict the singlet-triplet transitions of the effective
two-electron molecule as a function of the magnetic field, the number of
electrons, and confining potential using the configuration interaction method
(CI) coupled with the unrestricted Hartree-Fock (URHF) basis. In addition to
the singlet-triplet transitions of a 2 electron molecule involving edge states,
triplet transitions involving transfer of electrons to the center of individual
dots exist for .Comment: 5 pages, 10 figure
Optical control of internal electric fields in band-gap graded InGaN nanowires
InGaN nanowires are suitable building blocks for many future optoelectronic
devices. We show that a linear grading of the indium content along the nanowire
axis from GaN to InN introduces an internal electric field evoking a
photocurrent. Consistent with quantitative band structure simulations we
observe a sign change in the measured photocurrent as a function of photon
flux. This negative differential photocurrent opens the path to a new type of
nanowire-based photodetector. We demonstrate that the photocurrent response of
the nanowires is as fast as 1.5 ps
Covalently Binding the Photosystem I to Carbon Nanotubes
We present a chemical route to covalently couple the photosystem I (PS I) to
carbon nanotubes (CNTs). Small linker molecules are used to connect the PS I to
the CNTs. Hybrid systems, consisting of CNTs and the PS I, promise new
photo-induced transport phenomena due to the outstanding optoelectronic
properties of the robust cyanobacteria membrane protein PS I
Photoconductance of a submicron oxidized line in surface conductive single crystalline diamond
We report on sub-bandgap optoelectronic phenomena of hydrogen-terminated
diamond patterned with a submicron oxidized line. The line acts as an energy
barrier for the two-dimensional hole gas located below the hydrogenated diamond
surface. A photoconductive gain of the hole conductivity across the barrier is
measured for sub-bandgap illumination. The findings are consistent with
photogenerated electrons being trapped in defect levels within the barrier. We
discuss the spatial and energetic characteristics of the optoelectronic
phenomena, as well as possible photocurrent effects
Pinning a Domain Wall in (Ga,Mn)As with Focused Ion Beam Lithography
We utilize a focused beam of Ga+ ions to define magnetization pinning sites
in a ferromagnetic epilayer of (Ga,Mn)As. The nonmagnetic defects locally
increase the magneto-crystalline anisotropy energies, by which a domain wall is
pinned at a given position. We demonstrate techniques for manipulating domain
walls at these pinning sites as probed with the giant planar Hall effect
(GPHE). By varying the magnetic field angle relative to the crystal axes, an
upper limit is placed on the local effective anisotropy energy.Comment: 13 pages, 3 figure
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