Directional driving of vortex lines with oscillating magnetic field

Abstract

The possibility of driving vortex lines with an oscillating magnetic field could be useful in many applications. For example, it can be used for the removal of undesired trapped flux from contactless elements of superconducting devices. We investigate the dynamics of vortex lines in a superconducting film with a ratchet thickness profile driven by an oscillating magnetic field applied parallel to the film. We numerically simulate the dynamics of a single flux line modeled as an elastic string with a variable length. We explore the behavior for different frequencies and amplitudes of the oscillating magnetic field and find several dynamic regimes. For moderate frequencies, the average velocity is finite only within specific amplitude ranges. A notable feature is the presence of extended velocity plateaus, which correspond to regimes when the line moves by integer multiples of the spatial period $w$ during integer multiples of the time period $T$. The transitions to these plateau states are rather steep, especially at low frequencies. The plateau at velocity $w/T$ dominates at intermediate frequencies but vanishes at high frequencies. The onset field amplitude of finite velocity nonmonotonically depends on the frequency and passes through a minimum at a certain frequency value. At low frequencies, the velocity exceeds $w/T$ and progressively increases with the amplitude. These findings provide valuable insights into the dynamic behavior of vortex lines driven by oscillating magnetic field in patterned superconducting films, offering potential pathways for controlling the magnetic flux in superconducting devices.