NaFe0.56Cu0.44As: A Pnictide Insulating Phase Induced by On-Site Coulomb Interaction
NaFe0.56Cu0.44As: A Pnictide Insulating Phase Induced by On-Site Coulomb Interaction
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NaFe0.56Cu0.44As：现场库仑相互作用诱导的磷族化合物绝缘相
DOI：
10.1103/physrevlett.117.097001
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发表时间：
2016-08-25
影响因子：
8.6
通讯作者：
Shi, M.
中科院分区：
文献类型：
--
作者：
Matt, C. E.;Xu, N.;Shi, M.
在铁磷族化物的研究中，一个关键问题是产生超导性的不良金属态是否与磁有序绝缘相非常接近。最近发现，在低温下，重铜掺杂的NaFe1-xCuxAs (x > 0.3)铁磷族化合物是一种具有长程反铁磁序的绝缘体，类似于铜酸盐的母体化合物，但与所有其他磷族铁化合物不同。利用角分辨光电子能谱，我们确定了 NaFe1-xCuxAs (x = 0.44) 的动量分辨电子结构，并确定其基态是窄带隙绝缘体。结合实验结果与密度泛函理论（DFT）和DFT + U计算，我们的分析表明，现场库仑（Hubbard）和亨德耦合能在化学势带隙的形成中起着至关重要的作用。我们提出，在有限温度下，载流子被热激发，从类 Cu-As 价带进入具有类 Fe 3d 特征的导带。随着温度的升高，导带中的电子数量变多，Fe位点之间的跳跃能量增加，最终在T>T-N时长程反铁磁有序被破坏。我们的研究为研究莫特绝缘体电子结构转变为不良金属相并最终在铁磷化物中形成超导态的演化提供了基础。
In the studies of iron pnictides, a key question is whether their bad-metal state from which the superconductivity emerges lies in close proximity with a magnetically ordered insulating phase. Recently, it was found that at low temperatures, the heavily Cu-doped NaFe1-xCuxAs (x > 0.3) iron pnictide is an insulatorwith long-range antiferromagnetic order, similar to the parent compound of cuprates but distinct from all other iron pnictides. Using angle-resolved photoemission spectroscopy, we determined the momentumresolved electronic structure of NaFe1-xCuxAs (x = 0.44) and identified that its ground state is a narrow-gap insulator. Combining the experimental results with density functional theory (DFT) andDFT + U calculations, our analysis reveals that the on-site Coulombic (Hubbard) and Hund's coupling energies play crucial roles in the formation of the band gap about the chemical potential. We propose that at finite temperatures, charge carriers are thermally excited fromtheCu-As-likevalence band into the conduction band, which is of Fe 3d-like character. With increasing temperature, the number of electrons in the conduction band becomes larger and the hopping energy between Fe sites increases, and finally the long-range antiferromagnetic order is destroyed at T > T-N. Our study provides a basis for investigating the evolution of the electronic structure of aMott insulator transforming into a bad metallic phase and eventually forming a superconducting state in iron pnictides.