Fractal superconductivity near localization threshold
Fractal superconductivity near localization threshold
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DOI：
10.1016/j.aop.2010.04.001
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发表时间：
2010-07-01
影响因子：
3
通讯作者：
Cuevas, E.
中科院分区：
文献类型：
--
作者：
Feigel'man, M. V.;Ioffe, L. B.;Cuevas, E.
我们发展了一个半定量理论的电子配对和由此产生的超导体“不良导体”，其中费米能E-F是位于该地区的局域态不是那么远的安德森迁移率边缘E-C。我们假设费米面附近的电子之间存在吸引相互作用。我们回顾了现有的理论和实验数据，认为这一模型描述了一大类无序薄膜，我们的理论分析是基于对关联的解析处理，描述在3D安德森模型的精确单粒子本征态的基础上，我们联合收割机与本征函数关联的数值数据相结合。临界波函数的相关性的分形性质被证明是至关重要的这些系统的物理。我们确定了三个不同的阶段：“临界”超导态形成在E-F = E-C，超导态与一个强大的伪间隙，实现由于配对的弱本地化的电子和绝缘状态实现在EF更深的本地化带内。“临界”超导相的特征在于转变温度相对于BCS结果的提高，由非均匀的空间分布的有序参数和局域态密度。赝能隙态的主要新特征是存在两个独立的能量尺度：超导能隙δ，这是由于多体相关性和新的“伪能隙”能量标度Delta（P），该标度表征局域电子对的典型结合能，并导致电阻率作为高于超导T-c的温度的函数的绝缘行为伪能隙的两个能隙性质带隙的超导体显示出导致在扫描隧道光谱学和点接触Andreev光谱学中看到的特定特征。我们预言赝能隙超导态具有光谱权的反常行为。绝缘态是由于局域对隙的存在而实现的，但没有超导关联;它的特征是单电子密度中的硬绝缘间隙和类似于1/T的纯激活低温电阻率In R（T）。基于这些结果，我们提出了一种新的超导体“赝自旋”方案--绝缘体转变，并认为它是实现在一个特定的类别无序超导薄膜。最后，我们讨论的实验预测的理论和尚未解决的理论问题。(C)2010年爱思唯尔公司All rights reserved.
We develop a semi-quantitative theory of electron pairing and resulting superconductivity in bulk "poor conductors" in which Fermi energy E-F is located in the region of localized states not so far from the Anderson mobility edge E-c. We assume attractive interaction between electrons near the Fermi surface. We review the existing theories and experimental data and argue that a large class of disordered films is described by this model.Our theoretical analysis is based on analytical treatment of pairing correlations, described in the basis of the exact single-particle eigenstates of the 3D Anderson Model, which we combine with numerical data on eigenfunction correlations. Fractal nature of critical Wavefunction's correlations is shown to be crucial for the physics of these systems. We identify three distinct phases: 'critical' superconductive state formed at E-F = E-c, superconducting state with a strong pseudo-gap, realized due to pairing of weakly localized electrons and insulating state realized at EF still deeper inside a localized band. The 'critical' superconducting phase is characterized by the enhancement of the transition temperature with respect to BCS result, by the inhomogeneous spatial distribution of superconductive order parameter and local density of states. The major new feature of the pseudo-gapped state is the presence of two independent energy scales: superconducting gap Delta, that is due to many-body correlations and a new "pseudo-gap" energy scale Delta(P) which characterizes typical binding energy of localized electron pairs and leads to the insulating behavior of the resistivity as a function of temperature above superconductive T-c Two gap nature of the pseudo-gapped superconductor is shown to lead to specific features seen in scanning tunneling spectroscopy and point-contact Andreev spectroscopy. We predict that pseudo-gapped superconducting state demonstrates anomalous behavior of the optical spectral weight. The insulating state is realized due to the presence of local pairing gap but without superconducting correlations; it is characterized by a hard insulating gap in the density of single electrons and by purely activated low-temperature resistivity In R(T) similar to 1/T.Based on these results we propose a new "pseudo-spin" scenario of superconductor-insulator transition and argue that it is realized in a particular class of disordered superconducting films. We conclude by the discussion of the experimental predictions of the theory and the theoretical issues that remain unsolved. (C) 2010 Elsevier Inc. All rights reserved.