[论文解读] Fe-based high temperature superconductivity with Tc=31K bordering an insulating antiferromagnet in (Tl,K)FexSe2 Crystals

Minghu Fang, Hangdong Wang+5 more|arXiv (Cornell University)|Dec 23, 2010

Iron-based superconductors research参考文献 23被引用 204

一句话总结

本研究在接近绝缘反铁磁体的(Tl,K)FexSe2晶体中发现了Tc = 31 K的铁基高温超导，通过引入铁空位来调节电子关联作用。通过抑制磁序，超导态得以出现，表明强电子关联在铁基超导体中起着关键作用，该体系成为首个接近莫特绝缘态的铁基超导体。

ABSTRACT

Up to now, there have been two material families, the cuprates and the iron-based compounds with high-temperature superconductivity (HTSC). An essential open question is whether the two classes of materials share the same essential physics. In both, superconductivity (SC) emerges when an antiferromagnetical (AFM) ordered phase is suppressed. However, in cuprates, the repulsive interaction among the electrons is so strong that the parent compounds are "Mott insulators." By contrast, all iron-based parents are metallic. One perspective is that the iron-based parents are weakly correlated and that the AFM arises from a strong "nesting" of the Fermi surfaces. An alternative view is that the electronic correlations in the parents are still sufficiently strong to place the system close to the boundary between itinerancy and electronic localization. A key strategy to differentiate theses views is to explore whether the iron-based system can be tuned into a Mott insulator. Here we identify an insulating AFM in (Tl,K)FexSe2 by introducing Fe-vacancies and creating superconductivity in the Fe-planar. With the increasing Fe-content, the AFM order is reduced. When the magnetism is eliminated, a superconducting phase with Tc as high as 31K (and a Tc onset as high as 40K) is induced. Our findings indicate that the correlation effect plays a crucial role in the iron-based superconductors. (Tl,K)FexSe2, therefore, represents the first Fe-based high temperature superconductor near an insulating AFM.

研究动机与目标

• 确定铁基超导体是否可被调节至类似铜氧化物的莫特绝缘态。
• 通过探究接近绝缘反铁磁相的特性，研究电子关联在铁基超导体中的作用。
• 澄清铁基超导体的母相是弱关联性（由费米面嵌套驱动的磁性）还是强关联性（接近电子局域化）。
• 建立超导性与可调铁含量体系中反铁磁序抑制之间的直接联系。

提出的方法

• 通过控制铁空位浓度合成(Tl,K)FexSe2单晶，以调节电子结构。
• 利用电阻率、磁化率和比热测量探测反铁磁序和超导转变温度。
• 系统性地改变铁含量，追踪从反铁磁绝缘态到超导态的演化过程。
• 通过零电阻转变和迈斯纳效应测量确定超导转变温度（Tc）。
• 通过关联铁空位浓度与磁序抑制及超导出现的关系，分析相图。
• 将观测行为与强关联性与费米面嵌套的理论模型进行比较。

实验结果

研究问题

• RQ1 通过引入铁空位，能否将铁基超导体调节至莫特绝缘态？
• RQ2 在(Tl,K)FexSe2中，超导性的出现是否与反铁磁序的抑制同步发生？
• RQ3 基于接近绝缘反铁磁相的观测，电子关联在铁基超导体中扮演何种角色？
• RQ4 (Tl,K)FexSe2中的超导态是否在莫特相变附近稳定存在，表明强关联效应的存在？
• RQ5 在电子不稳定性方面，(Tl,K)FexSe2的相图与铜氧化物超导体的相图有何异同？

主要发现

• 在(Tl,K)FexSe2中引入铁空位可诱导从金属反铁磁态向绝缘反铁磁态的转变。
• 当反铁磁序被抑制时，超导态出现，Tc为31 K，Tc起始温度为40 K。
• 该体系在超导态与绝缘反铁磁态之间存在相边界，表明其接近莫特绝缘体。
• 在超导穹形区附近存在莫特绝缘相，为电子关联在铁基超导体中的重要性提供了有力证据。
• 所观测到的相图与铜氧化物超导体的相图高度相似，支持一种由关联驱动的电子不稳定性作为共同基础机制。
• 本工作确立了(Tl,K)FexSe2为首个接近绝缘反铁磁态的铁基高温超导体。