942 research outputs found

    Finite-temperature conductivity and magnetoconductivity of topological insulators

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    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 Ξ”(1232)\Delta(1232) Deformation

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    The two-photon-exchange (TPE) contribution in epβ†’epΟ€0ep\rightarrow ep\pi ^0 with W=MΞ”W=M_{\Delta} and small Q2Q^2 is calculated and its corrections to the ratios of electromagnetic transition form factors REM=E1+(3/2)/M1+(3/2)R_{EM} = E_{1+}^{(3/2)}/M_{1+}^{(3/2)} and RSM=S1+(3/2)/M1+(3/2)R_{SM} = S_{1+}^{(3/2)}/M_{1+}^{(3/2)}, 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 epβ†’epΟ€0ep\rightarrow ep\pi ^0 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 Q2<2Q^2<2 GeV2^2. It gives small correction to REMR_{EM} while for RSMR_{SM}, the correction is about -10\% at small Ο΅\epsilon and about 1%1\% at large Ο΅\epsilon for Q2β‰ˆ2.5Q^2\approx2.5 GeV2^2. The large correction from TPE at small Ο΅\epsilon must be included in the analysis to get a reliable extraction of RSMR_{SM}.Comment: Talk given at Conference:C16-07-2
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