274 research outputs found
Ultrafast helicity control of surface currents in topological insulators with near-unity fidelity
In recent years, a class of solid state materials, called three-dimensional
topological insulators, has emerged. In the bulk, a topological insulator
behaves like an ordinary insulator with a band gap. At the surface, conducting
gapless states exist showing remarkable properties such as helical Dirac
dispersion and suppression of backscattering of spin-polarized charge carriers.
The characterization and control of the surface states via transport
experiments is often hindered by residual bulk contributions yet at cryogenic
temperatures. Here, we show that surface currents in Bi2Se3 can be controlled
by circularly polarized light on a picosecond time scale with a fidelity near
unity even at room temperature. We re-veal the temporal separation of such
ultrafast helicity-dependent surface currents from photo-induced thermoelectric
and drift currents in the bulk. Our results uncover the functionality of
ultrafast optoelectronic devices based on surface currents in topological
insulators.Comment: 19 pages, 4 figures, supplementary informatio
Dicke effect in a quantum wire with side-coupled quantum dots
A system of an array of side-coupled quantum-dots attached to a quantum wire
is studied theoretically. Transport through the quantum wire is investigated by
means of a noninteracting Anderson tunneling Hamiltonian. Analytical
expressions of the transmission probability and phase are given. The
transmission probability shows an energy spectrum with forbidden and allowed
bands that depends on the up-down asymmetry of the system. In up-down symmetry
only the gap survives, and in up-down asymmetry an allowed band is formed. We
show that the allowed band arises by the indirect coupling between the up and
down quantum dots. In addition, the band edges can be controlled by the degree
of asymmetry of the quantum dots. We discuss the analogy between this
phenomenon with the Dicke effect in optics.Comment: 11 pages, 5 figures. To appear in Physica
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
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
Coulomb blockade double-dot Aharonov-Bohm interferometer: giant fluctuations
Electron transport through two parallel quantum dots is a kind of solid-state
realization of double-path interference. We demonstrate that the inter-dot
Coulomb correlation and quantum coherence would result in strong current
fluctuations with a divergent Fano factor at zero frequency. We also provide
physical interpretation for this surprising result, which displays its generic
feature and allows us to recover this phenomenon in more complicated systems.Comment: 5 pages, 4 figure
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