无序超导体磁通运动的两次退钉扎效应和重新进入超导相

Two-step depinning and reentrant superconducting phase of moving vortex lattice in disordered superconductors

考虑平面内和不同平面磁通之间的相互作用力,计算了无序各向异性超导体中磁通运动的平均速度、微分电阻随驱动力Fl的变化规律,用层间关联函数Cz的值来判断2D塑性流动和3D关联流动的运动图像.观察到随着外驱动力的增大微分电阻出现两个尖峰,它对应着磁通运动存在两次退钉扎现象.在一定层间耦合条件下,在微分电阻双峰之间,可观察到重新进入微分电阻为零的钉扎相.这与最近实验上新发现的无序弱钉扎超导体有重新进入超导相的巨大峰值效应相吻合.同时,也可发现随着驱动电流的增大,磁通运动出现由2D塑性流动到3D弹性流动的相变,这一维度的变化对应着微分电阻dV/dI曲线中的二次峰位置.并证明当层间耦合(即代表磁场的大小)在一定范围时,3D-2D相变对应的临界电流随磁场的增大而增大,反映了第二磁化峰附近的磁通格子软硬度改变的微观图像.

We developed a 3D flux-line lattice model with magnetic interactions between intraplane and interplane vortices to simulate the transport properties and the dynamic behavior of disordered anisotropic superconductors. We observed a double peak in the differential resistivity as the driving current increases, which corresponds to a two-step depinning in the vortex motion. Between the two peaks we also observed a reentering pinning phase. We also show that the transition from 2D plastic flow to 3D elastic flow of vortex motion is a recoupling transition which is associated with the double peak in differential resistivity. The increase of critical current of 3D-2D transition with the increasing of magnetic field （decreasing of relative interlayer coupling strength）, indicates of a second peak effect.