铁基超导体FeSe_(0.5)Te_(0.5)表面隧道谱的研究  

Investigation of scanning tunneling spectra on iron-based superconductor FeSe_(0.5)Te_(0.5)

作　　者：杜增义 方德龙[1] 王震宇[2] 杜冠[1] 杨雄[1] 杨欢[1] 顾根大 闻海虎[1] 

机构地区：[1]人工微结构科学与技术协同创新中心固体微结构国家实验室南京大学物理学院,南京210093 [2]中国科学院物理研究所超导国家重点实验室,北京100190 [3]美国布鲁克海文国家实验室凝聚态物理和材料科学系,美国纽约119735000

出　　处：《物理学报》2015年第9期73-79,共7页Acta Physica Sinica

基　　金：国家重点基础研究发展计划(批准号:2011CBA00102);国家自然科学基金(批准号:11374144);美国能源部材料科学与工程学部基础能源科学办公室(项目合同号:DE-AC02-98CH10886)资助的课题~~

摘　　要：用扫描隧道显微镜/谱仪仔细研究了铁基超导单晶FeSe0.5Te0.5样品的表面形貌和隧道谱,测量到了清晰的表面原子形貌和在空间比较稳定的隧道谱结构.在样品中测量的隧道谱零能态密度比较高,说明样品里面有比较强的非弹性准粒子散射.在正能5 mV附近有个较大的背景鼓包,这一背景在很高温度也未消失.空间中Se和Te集中的位置会带来高能背景的变化,超导能隙附近谱的形状大致相同.较强的非弹性准粒子散射破坏了超导的准粒子散射,因此没有在二维微分电导图中发现超导准粒子相干散射的特征亮斑.FeSe0.sTe0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tun- neling microscopy/spectroscopy （STM/STS） measurements in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73±0.03A which is consistent with the lattice constant 3.78/a. The Se and Te atoms with a height difference of about 0.35 A are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconducting state. According to the positions of coherence peaks, we determine the superconducting gap 2△=5.5 meV, and the reduced gap 2△/ksTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy Ω of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature Ω/ksTc ≈4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom c

关 键 词：铁基超导体 扫描隧道谱 非常规超导电性 

分 类 号：O511.3[一般工业技术—材料科学与工程]