9,493 research outputs found

    Effect of disorder outside the CuO2_{2} planes on TcT_{c} of copper oxide superconductors

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    The effect of disorder on the superconducting transition temperature TcT_{c} of cuprate superconductors is examined. Disorder is introduced into the cation sites in the plane adjacent to the CuO2_{2} planes of two single-layer systems, Bi2.0_{2.0}Sr1.6_{1.6}Ln0.4_{0.4}CuO6+δ_{6+\delta} and La1.85y_{1.85-y}Ndy_{y}Sr0.15_{0.15}CuO4_{4}. Disorder is controlled by changing rare earth (Ln) ions with different ionic radius in the former, and by varying the Nd content in the latter with the doped carrier density kept constant. We show that this type of disorder works as weak scatterers in contrast to the in-plane disorder produced by Zn, but remarkably reduces TcT_{c} suggesting novel effects of disorder on high-TcT_{c} superconductivity.Comment: 5 pages, 5 figures, to be published in Phys. Rev. Let

    Fast generation of stability charts for time-delay systems using continuation of characteristic roots

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    Many dynamic processes involve time delays, thus their dynamics are governed by delay differential equations (DDEs). Studying the stability of dynamic systems is critical, but analyzing the stability of time-delay systems is challenging because DDEs are infinite-dimensional. We propose a new approach to quickly generate stability charts for DDEs using continuation of characteristic roots (CCR). In our CCR method, the roots of the characteristic equation of a DDE are written as implicit functions of the parameters of interest, and the continuation equations are derived in the form of ordinary differential equations (ODEs). Numerical continuation is then employed to determine the characteristic roots at all points in a parametric space; the stability of the original DDE can then be easily determined. A key advantage of the proposed method is that a system of linearly independent ODEs is solved rather than the typical strategy of solving a large eigenvalue problem at each grid point in the domain. Thus, the CCR method significantly reduces the computational effort required to determine the stability of DDEs. As we demonstrate with several examples, the CCR method generates highly accurate stability charts, and does so up to 10 times faster than the Galerkin approximation method.Comment: 12 pages, 6 figure