Nonlinear dynamics and dissipation of a curvilinear vortex driven by a strong time-dependent Meissner current

Abstract

We report numerical simulations of large-amplitude oscillations of a trapped vortex line under a strong ac magnetic field H(t)=Hsinωt parallel to the surface. The power dissipated by an oscillating vortex segment driven by the surface ac Meissner currents was calculated by taking into account the nonlinear vortex line tension, vortex mass, and a nonlinear Larkin-Ovchinnikov (LO) viscous drag coefficient η(v). We show that the LO decrease of η(v) with the vortex velocity v can radically change the field dependence of the surface resistance Ri(H) caused by trapped vortices. At low frequencies, Ri(H) exhibits a conventional increase with H, but as ω increases, the surface resistance becomes a nonmonotonic function of H which decreases with H at higher fields. The effects of frequency, pin spacing, and the mean-free path li on the field dependence of Ri(H) were calculated. It is shown that, as the surface gets dirtier and li decreases, the anomalous drop of Ri(H) with H shifts to lower fields which can be much smaller than the lower critical magnetic field. Our numerical simulations also show that the LO decrease of η(v) with v can cause a vortex bending instability at high field amplitudes and frequencies, giving rise to the formation of dynamic kinks along the vortex. Measurements of Ri(H) caused by sparse vortices trapped perpendicular to the surface can offer opportunities to investigate an extreme nonlinear dynamics of vortices driven by strong current densities up to the depairing limit at low temperatures. The behavior of Ri(H), which can be tuned by varying the rf frequency or concentration of nonmagnetic impurities, is not masked by strong heating effects characteristic of dc or pulse transport measurements.

Source-reported materials — not catalogue approval

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