双带超导体的扩展Ginzburg-Landau形式
Extended Ginzburg-Landau formalism for two-band superconductors
摘要：
最近在MgB_2单晶中观察到的异常涡旋图案引起了人们对一种新的超导类型（命名为“1.5型”）的猜测。然而，严格应用标准的双带Ginzburg-Landau（GL）理论导致两个带的简单比例序参量-并且不支持“1.5型”行为。本文导出了两带纯s波超导体的推广GL形式（考虑了小参数t= 1- T/T_c下的所有次项），并指出两种凝聚体一般具有不同的空间尺度，差别只在T -> T_c的极限处消失。推广后的两带GL形式改进了GL理论在T_c以下的有效性，并建议重新考虑以前基于标准模型的计算。
英文摘要：
Recent observation of unusual vortex patterns in MgB_2 single crystals raised speculations about a new type of superconductivity (named "type-1.5"). However, the strict application of the standard two-band Ginzburg-Landau (GL) theory results in simply proportional order parameters of the two bands - and does not support the "type-1.5" behavior. Here we derive the extended GL formalism (accounting all terms of the next order over the small t= 1- T/T_c parameter) for a two-band clean s-wave superconductor and show that the two condensates generally have different spatial scales, with difference disappearing only in the limit T -> T_c. The extended version of the two-band GL formalism improves the validity of GL theory below T_c, and suggests revisiting of the earlier calculations based on the standard model.
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