942 research outputs found
Finite-temperature conductivity and magnetoconductivity of topological insulators
The electronic transport experiments on topological insulators exhibit a
dilemma. A negative cusp in magnetoconductivity is widely believed as a quantum
transport signature of the topological surface states, which are immune from
localization and exhibit the weak antilocalization. However, the measured
conductivity drops logarithmically when lowering temperature, showing a typical
feature of the weak localization as in ordinary disordered metals. Here, we
present a conductivity formula for massless and massive Dirac fermions as a
function of magnetic field and temperature, by taking into account the
electron-electron interaction and quantum interference simultaneously. The
formula reconciles the dilemma by explicitly clarifying that the temperature
dependence of the conductivity is dominated by the interaction while the
magnetoconductivity is mainly contributed by the quantum interference. The
theory paves the road to quantitatively study the transport in topological
insulators and other two-dimensional Dirac-like systems, such as graphene,
transition metal dichalcogenides, and silicene.Comment: 5 pages, 5 figure
Two-Photon-Exchange Effects and Deformation
The two-photon-exchange (TPE) contribution in with
and small is calculated and its corrections to the ratios
of electromagnetic transition form factors and ,
are analysed. A simple hadronic model is used to estimate the TPE amplitude.
Two phenomenological models, MAID2007 and SAID, are used to approximate the
full cross sections which contain both the TPE and the
one-photon-exchange (OPE) contributions. The genuine the OPE amplitude is then
extracted from an integral equation by iteration. We find that the TPE
contribution is not sensitive to whether MAID or SAID is used as input in the
region with GeV.
It gives small correction to while for , the correction is
about -10\% at small and about at large for
GeV. The large correction from TPE at small must
be included in the analysis to get a reliable extraction of .Comment: Talk given at Conference:C16-07-2
- β¦