Bi2Sr2CaCu2O8+x中轨道有序的发现
Discovery of Orbital Ordering in Bi2Sr2CaCu2O8+x
AI总结：
本研究将子晶格分辨E(r)成像技术用于欠掺杂CuO2研究，发现了Q=0的晶胞内轨道有序态，氧轨道能级分裂约50 meV，该态以无序伊辛畴排列，畴界由掺杂离子界定且存在低能电子四极二能级系统，验证了长期预测的晶胞内对称性破缺。
摘要：
铜氧化物超导的核心基础是CuO2晶胞。目前理论研究通常聚焦于主导每个铜离子3d^9和3d^10构型的原子内库仑相互作用。然而，若每个平面氧原子2p^6轨道的电子间也存在库仑相互作用，自发轨道有序可能会使其能级发生分裂。这种长期被预测的晶胞内对称性破缺应会产生轨道有序相，在该相中，分隔2p^6与3d^10轨道的电荷转移能E对两个氧原子而言是不同的。本文将子晶格分辨的E(r)成像技术引入CuO2研究，发现了E(r)的晶胞内旋转对称性破缺，两个氧原子间的能级分裂约为50 meV量级。在空间上，这种态以正交取向轨道有序的无序伊辛畴形式排列，畴界似乎由掺杂离子界定，且畴壁内存在低能电子四极二能级系统。总体而言，这些数据揭示了欠掺杂CuO2中存在一种Q=0的轨道有序态，它使氧轨道的能级分裂约50 meV。
英文摘要：
The primordial ingredient of cuprate superconductivity is the CuO2 unit cell. Here, theoretical attention usually concentrates on the intra-atom Coulombic interactions dominating the 3d^9 and 3d^10 configurations of each copper ion. However, if Coulombic interactions also occur between electrons of the 2p^6 orbitals of each planar oxygen atom, spontaneous orbital ordering may split their energy levels. This long predicted intra-unit cell symmetry breaking should then generate an orbital ordered phase, for which the charge-transfer energy E separating the 2p^6 and 3d^10orbitals is distinct for the two oxygen atoms. Here we introduce sublattice resolved E(r) imaging techniques to CuO2 studies and discover intra-unit-cell rotational symmetry breaking of E(r), with energy-level splitting between the two oxygen atoms on the 50 meV scale. Spatially, this state is arranged in disordered Ising domains of orthogonally oriented orbital order that appear bounded by dopant ions, and within whose domain walls low energy electronic quadrupolar two-level systems occur. Overall, these data reveal a Q=0 orbitally ordered state that splits the energy levels of the oxygen orbitals by ~50 meV, in underdoped CuO2.
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