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arXiv 1408.1633cond-mat.supr-con
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强磁场中双带超导体的涨落

Fluctuations in two-band superconductors in a strong magnetic field

A. E. Koshelev, A. A. Varlamov

摘要:

本文研究了双带超导体在上临界场线附近比热和电导率的涨落行为。当谱带具有非常不同的相干长度时,多谱带效应是显著的。到基态的跃迁主要取决于“强”带的刚性凝聚体的性质,而具有大相干长度的库珀对的“弱”带导致了涨落行为的非定域性,并导致了简单Ginzburg-Landau图像的崩溃。正如预期的那样,当磁场接近上临界场时,多带电子结构并不改变涨落校正的主导发散的函数形式。然而,系数的温度依赖性被修改。大的面内相干长度设定了上临界场具有向上曲率的场尺度。由于有效z轴相干长度的减小,在该场尺度下,波动幅度和波动宽度增大。我们还观察到,明显的运输过渡取代到较低的温度相对于热力学转变。即使这种效应已经存在于足够高场的单带情况下,它可能会在多带材料中强烈增强。

英文摘要:

We consider the behaviour of the fluctuating specific heat and conductivity in the vicinity of the upper critical field line for a two-band superconductor. Multiple-band effects are pronounced when the bands have very different coherence lengths. The transition to superconductive state is mainly determined by the properties of the rigid condensate of the "strong" band, while the "weak" band with a large coherence length of the Cooper pairs causes the nonlocality in fluctuation behaviour and break down of the simple Ginzburg-Landau picture. As expected, the multiple-band electronic structure does not change the functional forms of dominating divergencies of the fluctuating corrections when the magnetic field approaches the upper critical field. The temperature dependence of the coefficients, however, is modified. The large in-plane coherence length sets the field scale at which the upper critical field has upward curvature. The amplitude of fluctuations and fluctuation width enhances at this field scale due to reduction of the effective z-axis coherence length. We also observe that the apparent transport transition displaces to lower temperatures with respect to the thermodynamic transition. Even though this effect exists already in a single-band case at sufficiently high fields, it may be strongly enhanced in multiband materials.

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