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arXiv 0904.0746cond-mat.supr-con
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双组分超导中复合涡旋的表面能符号变化与稳定性

Sign change of surface energy and stability of composite vortex in two-component superconductivity

Jun-Ping Wang

摘要:

在双组分超导体中存在双组分稳定的复合涡旋可以形成独特的涡旋模式,并可能导致1.5型超导。本文研究了双组分超导体的表面能,指出表面能的符号不仅由两组分超导体的Ginzburg-Landau参数$κ_i (i=1,2)$决定,而且还由一个与温度无关的参数$κ_ξ$决定,该参数定义为两组分超导体的相干长度之比。由于负的表面能有利于超导体中热力学稳定的复合涡旋的侵入,因此,这三个独立的无量纲参数是复合涡旋稳定性的判据。我们发现,在1型+2型或2型+2型材料中,可以存在双稳复合涡。我们还预测,不寻常的旋涡图案,如在$MgB_2$中观察到的那些(V. Moshchalkov等人,Phys. Rev. Lett.,102,117001(2009))可以发生在一些2型+2型超导体中。

英文摘要:

Existence of thermodynamically stable composite vortices in a two-component superconductor may form distinctive vortex patterns, and may lead to type-1.5 superconductivity. Here we study the surface energy of the two-component superconductor and show that the sign of surface energy is determined not only by the Ginzburg-Landau parameters $κ_i (i=1,2)$ of two superconducting components, but also by a temperature independent parameter $κ_ξ$, which is defined as the ratio of the coherence lengths of two components. Since the negative surface energy conduces to the invasion of thermodynamically stable composite vortices into a superconductor, the criterions for stability of composite vortex are these three independent dimensionless parameters. We find that there can exist thermodynamically stable composite vortex in a type-1+type-2 or type-2+type-2 material. We also predict that unusual vortex patterns like those observed in $MgB_2$ (V. Moshchalkov et al, Phys. Rev. Lett., 102, 117001 (2009)) can occur in some type-2+type-2 superconductors.

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