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) = H sin ωt 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 increases 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. arXiv:2001.08836v1 [cond-mat.supr-con]

Effect of random pinning on nonlinear dynamics and dissipation of a vortex driven by a strong microwave current

“…1. In particular, we calculated the effect of the LO velocity dependence of η(v) on R i (H, ω) in a film with many pinning centers, extending our previous results for a vortex pinned by a single material defect 60 . We also addressed the overheating of a single moving vortex and its effect on the nonlinear vortex drag, as well as the effect of overheating of sparse vortices on the field and frequency dependencies of the global surface resistance.…”

“…Bending distortions of the vortex are small and the linear elasticity theory 5,6 can be used. The effect of nonlinear elasticity was addressed recently 60 . 5.…”

“…How could the decrease of η(v) with v manifest itself in the dependencies of R i (H, ω) on H, ω and pinning strength? For a vortex segment pinned by a single strong pin in the bulk, some of these issues were addressed previously 60 , and the effect of artificial pinning centers on the LO instability in films under a dc magnetic field and transport current was investigated in Refs. 89 and 90.…”

Rising speed limits for fluxons via edge quality improvement in wide MoSi thin films

“…Ultra-fast vortex motion in superconductors has recently attracted great attention both experimentally [1][2][3][4][5][6] and theoretically [7][8][9][10][11][12]. This attention is triggered by the fundamental question regarding the ultimate speed limit for magnetic flux transport via superconducting vortices and the phenomena of generation of sound [13,14] and spin waves [15,16] by fluxons moving at velocities of a few km/s.…”

“…The physical phenomenon underlying this judgement is known as the flux-flow instability (FFI) [1][2][3][4][5][6][7][8][9][10][11][12][22][23][24][25]. FFI occurs in the regime of fast vortex motion and, in the currentdriven regime, it becomes apparent as a sudden jump to a highly-resistive state in the current-voltage (I-V ) curve of the superconductor.…”