Current induced vortex nucleation in periodic 2-D superconducting hole arrays

In the presence of a periodic lattice of patterned pinning sites in a superconducting film, together with a proper choice of an external magnetic field, a commensurate vortex array can be prepared. Above some critical applied d.c. current the lattice breaks loose from these pins and drifts between them, momentarily repinning at each site. This generates an a.c. current in the film, the fundamental frequency of which increases with the applied d.c. current.  We have simulated this behavior using the time Dependent Ginzburg-Landau formalism (TDGL)† for arrays of circular pinning sites having differing diameters, pinning strengths and spacings. Depending on conditions, the harmonic content of the resulting signal can be high. If, in addition, an external a.c. current is superimposed on the d.c. current, the vortex site-hopping frequency can be pulled and locked to the applied frequency over some range of applied frequencies that depends on the strength of the a.c. current.

† A. Sadovskyy, A.E. Koshelev, C.L. Phillips, D.A. Karpeyev and A. Glatz, Journal of Computational Physics 294, 6391 (2015).