Instability and fluctuations of flux lines with point impurities in a parallel current

A parallel current can destabilize a single flux line (FL) or an array of F Ls. We consider the effects of pinning by point impurities on this instabil ity. The presence of impurities destroys the long-range order of a flux lat tice, leading to the so-called Bragg glass (BrG) phase. We first show that the long-range topological order of the BrG is also destroyed by a parallel current. Nonetheless, some degree of shea-range order should remain, whose destruction by thermal and impurity fluctuations, as well as the current, is studied here. To this end, we employ a cage model for a single FL in the presence of impurities and current, and study it analytically (by replica variational methods) and numerically (using a transfer matrix technique). T he results are in good agreement, and in conjunction with a Lindemann crite rion, provide the boundary in the magnetic-field-temperature plane for dest ruction of short-range order. In all cases, we find that the addition of im purities or current (singly or in combination) leads to a further increase in equilibrium FL fluctuations. Thus pinning to point impurities does not s tabilize FLs in a parallel current j(z), although the onset of this instabi lity is much delayed due to large potential barriers that diverge as j(z)(- mu).