To decipher the mechanism of high-temperature superconductivity, it is important to know how the superconducting pairing emerges from the unusual normal states of cuprate superconductors^1,2,3,4, including the pseudogap^5,6, strange metal^7,8 and anomalous Fermi liquid⁹ phases. A long-standing issue is how the superconducting pairing is formed and condensed in the strange metal phase, because this is where the superconducting transition temperature is highest. Here, we use state-of-the-art high-pressure measurements to report the experimental observation of a pressure-induced crossover from two- to three-dimensional (2D to 3D) superconducting states in optimally doped Bi₂Sr₂CaCu₂O_8 + δ bulk superconductor. By analysing the temperature dependence of the resistance, we find that the 2D superconducting transition exhibits a Berezinskii–Kosterlitz–Thouless-like behaviour¹⁰. The emergence of this 2D superconducting transition provides direct evidence that the strange metal state is predominantly 2D-like. This is important for a thorough understanding of the phase diagram of cuprate superconductors.

为了解释高温超导的机理，重要的是要了解铜质超导体^1,2,3,4的异常正常状态如何产生超导配对，其中铜态超导体^1,2,3,4包括伪间隙^5,6，奇异金属^7,8和异常费米液相⁹相。一个长期存在的问题是，如何在奇怪的金属相中形成和凝聚超导对，因为这是超导转变温度最高的地方。在这里，我们使用最先进的高压测量方法来报告在最佳掺杂的Bi ₂ Sr ₂ CaCu中压力诱导的从二维到三维（2D到3D）超导态交叉的实验观察。₂ O _{8 +  δ}体超导体。通过分析电阻的温度依赖性，我们发现二维超导转变表现出Berezinskii–Kosterlitz–Thouless行为¹⁰。2D超导跃迁的出现提供了直接的证据，证明奇怪的金属态主要是2D样的。这对于彻底了解铜酸盐超导体的相图非常重要。