Emergence of preformed Cooper pairs from the doped Mott insulating state in Bi2Sr2CaCu2O8+δ
Emergence of preformed Cooper pairs from the doped Mott insulating state in Bi2Sr2CaCu2O8+δ
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DOI：
10.1038/nature07400
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发表时间：
2008-11
期刊：
影响因子：
64.8
通讯作者：
H.-B. Yang;J. Rameau;P. Johnson;T. Valla;A. Tsvelik;G. Gu
中科院分区：
文献类型：
--
作者：
H.-B. Yang;J. Rameau;P. Johnson;T. Valla;A. Tsvelik;G. Gu
超导体的特征在于能隙，能隙表示将电子对（库珀对）分开所需的能量。在温度大大高于超导性，高转变温度的铜氧化物有一个额外的“赝隙”。目前还不清楚这是否代表了没有达到超导所需的相干性的预制电子对，或者它是否反映了与超导竞争的其他基态。成对的电子应该相对于费米能级（电子系统中最高占据能级的能量）表现出粒子-空穴对称性，但竞争态不需要表现出这种对称性。在这里，我们报告的光电子能谱研究的欠掺杂的铜氧化物Bi 2Sr 2CaCu 2 O 8 +δ，显示了一个对称的间隙只在反节点区域的开放，相反的预期，配对将发生在节点区域。因此，很明显，赝能隙确实反映了预先形成的电子对的形成，而且这种配对只发生在下面晶格的明确方向上。
Superconductors are characterized by an energy gap that represents the energy needed to break the pairs of electrons (Cooper pairs) apart. At temperatures considerably above those associated with superconductivity, the high-transition-temperature copper oxides have an additional ‘pseudogap’. It has been unclear whether this represents preformed pairs of electrons that have not achieved the coherence necessary for superconductivity, or whether it reflects some alternative ground state that competes with superconductivity. Paired electrons should display particle–hole symmetry with respect to the Fermi level (the energy of the highest occupied level in the electronic system), but competing states,,need not show such symmetry. Here we report a photoemission study of the underdoped copper oxide Bi2Sr2CaCu2O8+δthat shows the opening of a symmetric gap only in the anti-nodal region, contrary to the expectation that pairing would take place in the nodal region. It is therefore evident that the pseudogap does reflect the formation of preformed pairs of electrons and that the pairing occurs only in well-defined directions of the underlying lattice.