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Browsing by Author "Das, Jayajit"

Now showing 1 - 3 of 3
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    Dynamics of magnetic flux lines in the presence of correlated disorder
    Bullard, Thomas J. III; Das, Jayajit; Täuber, Uwe C. (2013-07-28)
    We investigate the dynamics of interacting magnetic flux lines driven by an external current in the presence of linear pinning centers, arranged either in a periodic square lattice or placed randomly in space, by means of three-dimensional Monte Carlo simulations. Compared to the non-interacting case, the repulsive forces between the vortices reduce the critical current J_c, as determined from the depinning threshold in the current-voltage (I-V) characteristics. Near the depinning current J_c, the voltage power spectrum S(w) reveals broad-band noise, characterized by a $1/w^a$ power law decay with a <= 2. At larger currents the flux lines move with an average velocity v_{cm}. For a periodic arrangement of columnar pins with a lattice constant $d$ and just above J_c, distinct peaks appear in the voltage noise spectrum S(w) at w ~ v_{cm}/d which we interpret as the signature of stick-slip flux line motion.
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    Vortex transport and voltage noise in disordered superconductors
    Das, Jayajit; Bullard, Thomas J. III; Täuber, Uwe C. (Elsevier, 2003-02-01)
    We study, by means of three-dimensional Monte Carlo simulations, the current–voltage (I–V) characteristics and the voltage noise spectrum at low temperatures of driven magnetic flux lines interacting with randomly placed point or columnar defects, as well as with periodically arranged linear pinning centers. Near the depinning current Jc, the voltage noise spectrum S(ω) universally follows a 1/ωα power law. For currents J>Jc, distinct peaks appear in S(ω) which are considerably more pronounced for extended as compared to point defects, and reflect the spatial distribution of the correlated pinning centers.
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    Vortex washboard voltage noise in type-II superconductors
    Bullard, Thomas J. III; Das, Jayajit; Daquila, George L.; Täuber, Uwe C. (Springer, 2008-10-01)
    In order to characterize flux flow through disordered type-II superconductors, we investigate the effects of columnar and point defects on the vortex velocity / voltage power spectrum in the driven non-equilibrium steady state. We employ three-dimensional Metropolis Monte Carlo simulations to measure relevant physical observables including the force-velocity / current-voltage (I-V) characteristics, vortex spatial arrangement and structure factor, and mean flux line radius of gyration. Our simulation results compare well to earlier findings and physical intuition. We focus specifically on the voltage noise power spectra in conjunction with the vortex structure factor in the presence of weak columnar and point pinning centers. We investigate the vortex washboard noise peak and associated higher harmonics, and show that the intensity ratios of the washboard harmonics are determined by the strength of the material defects rather than the type of pins present. Through varying columnar defect lengths and pinning strengths as well as magnetic flux density we further explore the effect of the material defects on vortex transport. It is demonstrated that the radius of gyration displays quantitatively unique features that depend characteristically on the type of material defects present in the sample.