Shi-Zeng Lin, Lev N. Bulaevskii
We propose to use superconductor-magnet multi-layer structure to achieve high critical current density. The magnetic layers have large magnetic susceptibility to enhance the coupling between vortices and magnetization. Meanwhile the relaxation of the magnetization is slow to retard the vortex motion. When the velocity of vortex is small, the vortex is dressed with magnetization and they move as a whole as a polaron. The viscosity of the whole system is enhanced significantly and is proportional to the magnetic relaxation time. For a large velocity, the polaron dissociates associated with a jump in the I-V curve. The corresponding current at the jump is the depinning current. For Nb and proper magnet multi-layer structure, we estimate the critical current density $J_c\sim 10^{9}\ \rm{A/m^2}$ at magnetic field $B\approx 1$ T.
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http://arxiv.org/abs/1206.6929
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