Optimally doped ceramic superconductors (cuprates, pnictides, etc.) exhibit transition temperatures T c much larger than strongly coupled metallic superconductors like Pb (T c = 7.2 K, E g/kT c = 4.5) and exhibit many universal features that appear to contradict the Bardeen, Cooper, and Schrieffer theory of superconductivity based on attractive electron-phonon pairing interactions. These complex materials are strongly disordered and contain several competing nanophases that cannot be described effectively by parameterized Hamiltonian models, yet their phase diagrams also exhibit many universal features in both the normal and superconductive states. Here we review the rapidly growing body of experimental results that suggest that these anomalously universal features are the result of marginal stabilities of the ceramic electronic and lattice structures. These dual marginal stabilities favor both electronic percolation of a dopant network and rigidity percolation of the deformed lattice network. This “double percolation” model has previously explained many features of the normal-state transport properties of these materials and is the only theory that has successfully predicted strict lowest upper bounds for T c in the cuprate and pnictide families. Here it is extended to include Coulomb correlations and percolative band narrowing, as well as an angular energy gap equation, which rationalizes angularly averaged gap/T c ratios, and shows that these are similar to those of conventional strongly coupled superconductors.
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机译：最佳掺杂的陶瓷超导体（铜酸盐，磷化物等）的转变温度T c比Pb等强耦合金属超导体大得多（T c = 7.2 K，E g / kT c = 4.5），并且表现出许多似乎矛盾的通用特征Bardeen，Cooper和Schrieffer的超导理论基于有吸引力的电子-声子配对相互作用。这些复杂的材料非常无序，包含几个竞争性的纳米相，无法通过参数化的哈密顿量模型有效地描述，但是它们的相图在常态和超导状态下也显示出许多通用特征。在这里，我们回顾了迅速增长的实验结果，这些结果表明这些异常通用的特征是陶瓷电子结构和晶格结构的边际稳定性的结果。这些双重边缘稳定性有利于掺杂剂网络的电子渗透和变形晶格网络的刚性渗透。这种“双重渗滤”模型先前已经解释了这些材料的正常状态传输特性的许多特征，并且是唯一成功预测铜酸盐和磷化物族中T c的严格最低上限的理论。在这里，它扩展为包括库仑相关性和渗透带变窄，以及角能隙方程，该方程合理化了角平均间隙/ T c比，并表明它们与常规的强耦合超导体相似。
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