CAJ | 학술논문

用扫描隧道显微镜／谱仪仔细研究了铁基超导单晶FeSe0.5 Te0.5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5mV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.
용소묘수도현미경／보의자세연구료철기초도단정FeSe0.5 Te0.5양품적표면형모화수도보，측량도료청석적표면원자형모화재공간비교은정적수도보결구．재양품중측량적수도보령능태밀도비교고，설명양품리면유비교강적비탄성준입자산사.재정능5mV부근유개교대적배경고포，저일배경재흔고온도야미소실.공간중Se화Te집중적위치회대래고능배경적변화，초도능극부근보적형상대치상동.교강적비탄성준입자산사파배료초도적준입자산사，인차몰유재이유미분전도도중발현초도준입자상간산사적특정량반.
FeSe0.5Te0.5 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±0.03 ? which is consistent with the lattice constant 3.78 ?. The Se and Te atoms with a height difference of about 0.35 ? 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?/kBTc =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?of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature ?/kBTc ≈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 cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.