The Bardeen–Cooper–Schrieffer theory of superconductivity and the Landau–Fermi liquid theory form the basis of our current understanding of conventional superconductors and their parent non-superconducting phases. However, some exotic superconductors do not conform to this physical picture but instead feature an unusual ‘normal’ state that is not a Fermi liquid. One explanation of this unusual behaviour is that pre-formed pairs of electrons are established above the superconducting temperature T_c. Here, we highlight recent experiments that show the likely existence of these pre-formed pairs in two rather different materials—a high-temperature cuprate superconductor and strontium titanate. Moreover, in both materials the normal state from which superconductivity emerges has other shared properties, including a pseudogap and electronic nematicity—rotational symmetry breaking in the electron fluid that is not expected in Fermi liquid theory nor more generally from the crystal lattice symmetry. These experimental findings should provoke more interaction between the communities working on these materials and new insights into the underlying mechanism of the creation of pre-formed pairs.

Bardeen-Cooper-Schrieffer超导理论和Landau-Fermi液体理论构成了我们目前对常规超导体及其母体非超导相的理解的基础。但是，一些奇特的超导体不符合这种物理图像，而是具有非正常的非费米液体“正常”状态。这种异常行为的一种解释是，在超导温度T _c之上会形成预先形成的电子对。在这里，我们重点介绍了最近的实验，这些实验显示了在两种相当不同的材料（高温铜酸盐超导体和钛酸锶）中这些预成型对的可能存在。此外，在这两种材料中，从中出现超导性的正常状态还具有其他共有的特性，包括伪间隙和电子向列性-电子流体中的旋转对称性破坏，这在费米液体理论中是无法预料的，​​更普遍地说是从晶格对称性中无法预测的。这些实验结果应会激发从事这些材料研究的社区之间的更多互动，以及对创建预制对的潜在机制的新见解。