具有慢磁弛豫动力学和大磁化率的超导/磁性多层膜临界电流密度的提高
Enhancement of critical current density in superconducting/magnetic multi-layers with slow magnetic relaxation dynamics and large magnetic susceptibility
摘要：
我们提出使用超导体-磁体多层结构，通过激发极化子钉扎机制来获得高临界电流密度。磁性层应该具有大的磁化率，以增强磁性层中的涡旋和磁化之间的耦合。磁化的弛豫应该是缓慢的。当涡旋速度较低时，它们被非均匀磁化修饰，并以极化子的形式运动。在这种情况下，与磁弛豫时间成正比的涡旋的粘性显著增强。随着速度的增加，极化子离解，粘度下降到通常的Bardeen-Stephen 1，导致I-V曲线跳跃。实验上，跳跃表现为脱钉过渡，并且跳跃处的相应电流是脱钉电流。对于Nb和适当的磁体多层结构，我们估计了磁场$B\approx 1$ T下的临界电流密度$J_c\sim 10^{9}\ \rm{A/m^2}$。
英文摘要：
We propose to use superconductor-magnet multi-layer structure to achieve high critical current density by invoking polaronic mechanism of pinning. The magnetic layers should have large magnetic susceptibility to enhance the coupling between vortices and magnetization in magnetic layers. The relaxation of the magnetization should be slow. When the velocity of vortices is low, they are dressed by nonuniform magnetization and move as polarons. In this case, the viscosity of vortices proportional to the magnetic relaxation time is enhanced significantly. As velocity increases, the polarons dissociate and the viscosity drops to the usual Bardeen-Stephen one, resulting in a jump in the I-V curve. Experimentally the jump shows up as a depinning transition and 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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