铁基超导体中的玻色模和超导电性的密切关系

铁基超导材料作为一类新的高温超导材料,其超导产生的原因一直备受关注,超导电子配对的机制一直是铁基超导研究中最具有挑战性的重大科学问题。目前有一个争论的焦点是,该类超导体是否仍然可以用BCS理论的延时电子和玻色子之间的相互作用来描述。我们通过扫描隧道谱仪,对两个不同铁基超导体系的样品进行了测量,发现除了超导特征的谱形之外,还有另一个特征峰,即玻色模,在两个样品中波色模的特征能量与中子自旋共振得到的能量数值相同,与超导临界温度之间呈现一个线性关系Ω/kBTc≈4.3±0.5。玻色模的特征峰与超导电性密切相关,并随着超导特征的减弱而减弱。上述研究结果揭示了铁基超导的非常规超导电性。

Close Relationship between Superconductivity and the Bosonic Mode in Iron Pnictide Superconductors

Since the discovery of high temperature supercon- ductivity in the iron pnictides and chalcogenides in early2008, it remains to be a challenging issue what makes the superconducting pairing. There is a debate at this moment about whether the pairing is due to a retarded electron-boson interaction, like in the conventional pho- non-mediated superconductors, although here the bosons may be the antiferromagnetic spin fluctuations. In this paper, based on the measurements of scanning tunneling spectroscopy, we show the clear evidence of the bosonic mode with the energy identical to that of the neutron resonance in two completely different systems Ba0.6K0.4Fe2As2 and Na（ Fe0.975Co0.025 ）As with different transition temperatures. In both samples, the superco ducting coherence peaks and the mode feature vanish simultaneously inside the vortex core or above To, indicating a close relationship between superconductivity and the bosonic mode. Our data also demonstrate a universal ratio between the mode energy and superconduct-ing transition temperature, that isΩ/kBTc≈4.3±0.5, which underlines the unconventional mechanism of su-perconductivity in the iron pnictide superconductors.