2,228,072 research outputs found
Frequency Scaling of Microwave Conductivity in the Integer Quantum Hall Effect Minima
We measure the longitudinal conductivity at frequencies GHz over a range of temperatures K with particular emphasis on the Quantum Hall plateaus. We find that
scales linearly with frequency for a range of magnetic field
around the center of the plateaus, i.e. where . The width of this scaling region decreases with higher
temperature and vanishes by 1.2 K altogether. Comparison between localization
length determined from and DC measurements on the same
wafer show good agreement.Comment: latex 4 pages, 4 figure
Profile statt Rankings: Eine Methode zur Darstellung von Aktivitäten institutioneller Einheiten der Kommunikationswissenschaft
Evaluationen und Rechenschaftspflicht für Forschende nehmen im Hochschulumfeld zu; gerade in Feldern der Geistes- und Sozialwissenschaften stoßen die klassischen Instrumente – oft auf der Basis bibliometrischer Analysen – auf Grenzen, da sie wichtige Eigenschaften der Felder, wie z. B. die Ausrichtung auf das lokale und sprachregionale Umfeld, die hohe Lehrbelastung oder das Gewicht der Publikationen in Buchform nicht berücksichtigen. In diesem Text stellen wir ein Instrument vor, das entwickelt wurde, um den Forschungsoutput kommunikationswissenschaftlicher Einheiten an Schweizer Hochschulen darzustellen. Dieses Instrument erstellt Forschungsprofile, welche die Aktivitäten in verschiedenen Dimensionen – Wissenschaft, Forschungsausbildung, Lehre und Transfer – abbilden. Solche Profile können als Grundlage für interne Standortbestimmungen, aber auch als Input für (Selbst-)Evaluationen verwendet werden. Der Text präsentiert das Instrument und diskutiert Herausforderungen bei seiner Erstellung und Implementation, illustriert anhand von Resultaten der Studie
Delocalized Chern character for stringy orbifold K-theory
In this paper, we define a stringy product on K^*_{orb}(\XX) \otimes \C ,
the orbifold K-theory of any almost complex presentable orbifold \XX. We
establish that under this stringy product, the de-locaized Chern character
ch_{deloc} : K^*_{orb}(\XX) \otimes \C \longrightarrow H^*_{CR}(\XX), after a
canonical modification, is a ring isomorphism. Here H^*_{CR}(\XX) is the
Chen-Ruan cohomology of \XX. The proof relies on an intrinsic description of
the obstruction bundles in the construction of Chen-Ruan product. As an
application, we investigate this stringy product on the equivariant K-theory
of a finite group with the conjugation action. It turns out that
the stringy product is different from the Pontryajin product (the latter is
also called the fusion product in string theory).Comment: 34 pages. Final version to appear in Trans. of AMS. Improve the
expositions and Change of the title thanks the referee
Radiative corrections to the excitonic molecule state in GaAs microcavities
The optical properties of excitonic molecules (XXs) in GaAs-based quantum
well microcavities (MCs) are studied, both theoretically and experimentally. We
show that the radiative corrections to the XX state, the Lamb shift
and radiative width , are
large, about of the molecule binding energy , and
definitely cannot be neglected. The optics of excitonic molecules is dominated
by the in-plane resonant dissociation of the molecules into outgoing
1-mode and 0-mode cavity polaritons. The later decay channel,
``excitonic molecule 0-mode polariton + 0-mode
polariton'', deals with the short-wavelength MC polaritons invisible in
standard optical experiments, i.e., refers to ``hidden'' optics of
microcavities. By using transient four-wave mixing and pump-probe
spectroscopies, we infer that the radiative width, associated with excitonic
molecules of the binding energy meV, is
meV in the microcavities and
meV in a reference GaAs single quantum
well (QW). We show that for our high-quality quasi-two-dimensional
nanostructures the limit, relevant to the XX states, holds at
temperatures below 10 K, and that the bipolariton model of excitonic molecules
explains quantitatively and self-consistently the measured XX radiative widths.
We also find and characterize two critical points in the dependence of the
radiative corrections against the microcavity detuning, and propose to use the
critical points for high-precision measurements of the molecule bindingenergy
and microcavity Rabi splitting.Comment: 16 pages, 11 figures, accepted for publication in Phys. Rev.
- …