Browsing by Subject "Linear response"

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    Drude and Superfluid Weights in Extended Systems: The Role of Discontinuities and δ-Peaks in the One-and Two-Body Momentum Densities
    (Institute of Pure and Applied Physics, 2012-01-05) Hetenyi, B.
    The question of conductivity is revisited. Using the total momentum shift operator to construct the perturbed many-body Hamiltonian and ground state wave function the second derivative of the ground state energy with respect to the perturbing field is expressed in terms of the one and two-body momentum densities. The distinction between the adiabatic and envelope function derivatives, hence that between the Drude and superfluid weights, can be introduced in a straightforward manner. It is shown that a discontinuity in the momentum density leads to a contribution to the Drude weight, but not the superfluid weight, however a delta-function contribution in the two-body momentum density (such as in the BCS wave-funtion) contributes to both quantities. The connection between the discontinuity in the momentum density and localization is also demonstrated.
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    Flexible metamaterials for wireless strain sensing
    (American Institute of Physics, 2009-11-04) Melik, R.; Unal, E.; Perkgoz, N. K.; Puttlitz, C.; Demir, Hilmi Volkan
    We proposed and demonstrated flexible metamaterial-based wireless strain sensors that include arrays of split ring resonators (SRRs) to telemetrically measure strain. For these metamaterial sensors, we showed that a flexible substrate (e.g., Kapton tape) delivers greater sensitivity and a more linear response as compared to using silicon substrates. Specifically, these tape-based flexible SRR sensors exhibit a significantly improved sensitivity level of 0.292 MHz/kgf with a substantially reduced nonlinearity error of 3% for externally applied mechanical loads up to 250 kgf. These data represent a sixfold increase in sensitivity and a 16-fold reduction in error percentage.
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    Nonequilibrium fractional Hall response after a topological quench
    (American Physical Society, 2016) Ünal, F. N.; Mueller, E. J.; Oktel, M. O.
    We theoretically study the Hall response of a lattice system following a quench where the topology of a filled band is suddenly changed. In the limit where the physics is dominated by a single Dirac cone, we find that the change in the Hall conductivity is two-thirds of the quantum of conductivity. We explore this universal behavior in the Haldane model and discuss cold-atom experiments for its observation. Beyond the linear response, the Hall effect crosses over from fractional to integer values. We investigate finite-size effects and the role of harmonic confinement.