电子掺杂的NaFeAs体系的配对对称性研究.pdf

摘 要 配对的对称性是超导研究中的一个关键问题。角分辨光电子能谱可以直接 测量样品的能隙,找出能隙随动量方向的变化,得到配对的对称性。本论文将 阐明我们用角分辨光电子能谱对 NaFe Co As 样品的研究结果。 0.95 0.05 铁基超导体是铜氧化物高温超导体后发现的另一类新型超导体。目前发现 的铁基超导体有四个体系: “1111”体系, “122”体系, “111”体系和“11”体 系。研究表明,其超导机理与Fe的3d轨道和FeAs层密切相关,Fe的3d轨道 全都靠近费米面,在费米面以下,与As的p轨道有着较大的重合,这样,扩大 了d电子的巡游性。我们用高分辨的角分辨光电子能谱对“111”体系中昀佳掺杂的 NaFe Co As 样品(Tc18K)进行了研究。发现在布厘渊区的高对称性点 ?, 0.95 0.05 M处分别有一个空穴型费米面和一个电子型费米面,当温度降低到超导转变温度 以下时,两个费米面均有约 6-7meV 的能隙打开。2/kT 值约为 8,证明该材 bc 料属于强关联体系。我们又测量了能隙随动量方向的变化,发现该材料的配对 对称性属于各项同性的S波配对。 关键词:NaFe Co As,能隙,角分辨光电子能谱,配对对称性 0.95 0.05 1AbstractPairing symmetry is one of the key question in superconductors research.Angle-resolved photoemission spectroscopy ARPES can measure the gaps directly,and get its change along the momentum,that get its paring symmetry.We will introduction our research result that we use ARPES sutdy on NaFe Co As 0.95 0.05 sample in this thesisIron-based superconductors is a newly system after Cuprate superconductors.And it contain four system:“1111”system , “122”system , “111”system和“11”system. Research evidence suggests that 3d electron of Fe and the FeAs layers play a key role in these superconductors,and all its orbits of 3d electron near the Fermi surface.There is a large overlap with p orbits of As above Fermi surface,So it is very itineraryWe have performed a high-resolution angle-resolved photoelectron spectroscopy study on the optimally doped NaFe Co As compoundTc 18 0.95 0.05 K.Below the superconducting transition temperatureTc18K,We have observed two superconducting gaps with same values,about 6-7meV, corresponding two Fermi surface around highly symmetry point in Brillouin zone: one hole-like Fermi surface nearpoint and another electron-like Fermi surface near M point.The ratio2/kT is about 8, that proved it is a strong correlation system.We also measured bc the gaps change along the momentum, and we find both gaps is likely isotropic S wave pairing Key words:NaFe Co As, gap, ARPES, paring symmetry 0.95 0.051 目 录