768 research outputs found
Orbital photogalvanic effects in quantum-confined structures
We report on the circular and linear photogalvanic effects caused by
free-carrier absorption of terahertz radiation in electron channels on
(001)-oriented and miscut silicon surfaces. The photocurrent behavior upon
variation of the radiation polarization state, wavelength, gate voltage and
temperature is studied. We present the microscopical and phenomenological
theory of the photogalvanic effects, which describes well the experimental
results. In particular, it is demonstrated that the circular (photon-helicity
sensitive) photocurrent in silicon-based structures is of pure orbital nature
originating from the quantum interference of different pathways contributing to
the absorption of monochromatic radiation.Comment: 8 pages, 5 figures, two culumne
Photon helicity driven electric currents in graphene
We report on the observation of photon helicity driven currents in graphene.
The directed net electric current is generated in single layer graphene by
circularly polarized terahertz laser radiation at normal as well as at oblique
incidence and changes its sign upon reversing the radiation helicity. The
phenomenological and microscopic theories of the observed photocurrents are
developed. We demonstrate that under oblique incidence the current is caused by
the circular photon drag effect in the interior of graphene sheet. By contrast,
the effect at normal incidence stems from the sample edges, which reduce the
symmetry and result in an asymmetric scattering of carriers driven by the
radiation field. Besides a photon helicity dependent current we also observe
photocurrents in response to linearly polarized radiation. The microscopic
mechanisms governing this effect are discussed.Comment: 13 pages, 7 figure
Chaos or Noise - Difficulties of a Distinction
In experiments, the dynamical behavior of systems is reflected in time
series. Due to the finiteness of the observational data set it is not possible
to reconstruct the invariant measure up to arbitrary fine resolution and
arbitrary high embedding dimension. These restrictions limit our ability to
distinguish between signals generated by different systems, such as regular,
chaotic or stochastic ones, when analyzed from a time series point of view. We
propose to classify the signal behavior, without referring to any specific
model, as stochastic or deterministic on a certain scale of the resolution
, according to the dependence of the -entropy,
, and of the finite size Lyapunov exponent,
, on .Comment: 24 pages RevTeX, 9 eps figures included, two references added, minor
corrections, one section has been split in two (submitted to PRE
Spin polarized electric currents in semiconductor heterostructures induced by microwave radiation
We report on microwave (mw) radiation induced electric currents in
(Cd,Mn)Te/(Cd,Mg)Te and InAs/(In,Ga)As quantum wells subjected to an external
in-plane magnetic field. The current generation is attributed to the
spin-dependent energy relaxation of electrons heated by mw radiation. The
relaxation produces equal and oppositely directed electron flows in the spin-up
and spin-down subbands yielding a pure spin current. The Zeeman splitting of
the subbands in the magnetic field leads to the conversion of the spin flow
into a spin-polarized electric current.Comment: 3 pages, 4 figure
Lab::Measurement - A portable and extensible framework for controlling lab equipment and conducting measurements
Lab::Measurement is a framework for test and measurement automatization using
Perl 5. While primarily developed with applications in mesoscopic physics in
mind, it is widely adaptable. Internally, a layer model is implemented.
Communication protocols such as IEEE 488, USB Test & Measurement, or, e.g.,
VXI-11 are addressed by the connection layer. The wide range of supported
connection backends enables unique cross-platform portability. At the
instrument layer, objects correspond to equipment connected to the measurement
PC (e.g., voltage sources, magnet power supplies, multimeters, etc.). The
high-level sweep layer automates the creation of measurement loops, with
simultaneous plotting and data logging. An extensive unit testing framework is
used to verify functionality even without connected equipment. Lab::Measurement
is distributed as free and open source software.Comment: Published version (open access, CC BY 4.0). 7 pages; refers to
Lab::Measurement 3.660, see https://www.labmeasurement.de
- …