Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, Japan.
Nat Commun. 2013;4:1815. doi: 10.1038/ncomms2805.
An energy gap is, in principle, a dominant parameter in superconductivity. However, this view has been challenged for the case of high-Tc cuprates, because anisotropic evolution of a d-wave-like superconducting gap with underdoping has been difficult to formulate along with a critical temperature Tc. Here we show that a nodal-gap energy 2ΔN closely follows 8.5 kBTc with underdoping and is also proportional to the product of an antinodal gap energy Δ(*) and a square-root superfluid density √Ps for Bi₂Sr₂CaCu₂O₈+δ, using low-energy synchrotron-radiation angle-resolved photoemission. The quantitative relations imply that the distinction between the nodal and antinodal gaps stems from the separation of the condensation and formation of electron pairs, and that the nodal-gap suppression represents the substantial phase incoherence inherent in a strong-coupling superconducting state. These simple gap-based formulae reasonably describe a crucial part of the unconventional mechanism governing Tc.
在原则上，能隙是超导性的一个主要参数。然而，这种观点已经受到了高温铜氧化物的挑战，因为随着欠掺杂，d 波类似超导能隙的各向异性演化与临界温度 Tc 很难结合在一起。在这里，我们利用低能同步辐射角分辨光发射谱表明，在 Bi₂Sr₂CaCu₂O₈+δ中，节点能隙 2ΔN 与欠掺杂时的 8.5 kBTc 密切相关，并且与反节点能隙 Δ(*)和平方根超导密度 √Ps 的乘积成正比。这些定量关系表明，节点和反节点能隙的区别源于电子对凝聚和形成的分离，而节点能隙的抑制代表了强耦合超导态中固有的实质性相位失谐。这些基于能隙的简单公式合理地描述了控制 Tc 的非常规机制的关键部分。
