Topological superconductors should be able to provide essential ingredients for quantum computing, but are very challenging to realize. Spin–orbit interaction in iron-based superconductors opens the energy gap between the p-states of pnictogen and d-states of iron very close to the Fermi level, and such p-states have been recently experimentally detected. Density-functional theory predicts existence of topological surface states within this gap in FeTe_1−xSe_x making it an attractive candidate material. Here we use synchrotron-based angle-resolved photoemission spectroscopy and band structure calculations to demonstrate that FeTe_1−xSe_x (x = 0.45) is a superconducting 3D Dirac semimetal hosting type-I and type-II Dirac points and that its electronic structure remains topologically trivial. We show that the inverted band gap in FeTe_1−xSe_x can possibly be realized by further increase of Te content, but strong correlations reduce it to a sub-meV size, making the experimental detection of this gap and corresponding topological surface states very challenging, not to mention exact matching with the Fermi level. On the other hand, the p–d and d–d interactions are responsible for the formation of extremely flat band at the Fermi level pointing to its intimate relation with the mechanism of high-T_c superconductivity in IBS.

拓扑超导体应该能够为量子计算提供必要的成分，但是要实现这一点非常具有挑战性。铁基超导体中的自旋-轨道相互作用打开了光生原的p-态与非常接近费米能级的铁的d-态之间的能隙，并且最近已经通过实验检测到了这种p-态。密度泛函理论预测FeTe _{1- x} Se _x的该间隙内存在拓扑表面状态，这使其成为有吸引力的候选材料。在这里，我们使用基于同步加速器的角度分辨光发射光谱和能带结构计算来证明FeTe _{1- x} Se _x（x  = 0.45）是一种超导电3D Dirac半金属，具有I型和II型Dirac点，其电子结构在拓扑上仍然无关紧要。我们表明，FeTe _{1- x} Se _x中的倒带隙可以通过进一步增加Te含量来实现，但是强相关性将其减小到亚meV大小，这使得该间隙和相应拓扑表面状态的实验检测变得非常容易具有挑战性，更不用说与费米水平的精确匹配了。另一方面，p – d和d – d相互作用是费米能级形成极平坦带的原因，表明它与IBS中高T _c超导机制密切相关。