The interest in Fe-chalcogenide unconventional superconductors is intense after the critical temperature of FeSe was reported enhanced by more than one order of magnitude in the monolayer limit at the interface to an insulating oxide substrate. In heterostructures comprising interfaces of FeSe with topological insulators, additional interesting physical phenomena is predicted to arise e.g. in form of {\it topological superconductivity}. So far superconductive properties of Fe-chalcogenide monolayers were mostly studied by local scanning tunneling spectroscopy experiments, which can detect pseudo-gaps in the density of states as an indicator for Cooper pairing. Direct macroscopic transport properties which can prove or falsify a superconducting phase were rarely reported due to the difficulty to grow films with homogeneous material properties. Here we report on a promising growth method to fabricate continuous carpets of monolayer thick FeSe on molecular beam epitaxy grown Bi$_2$Se$_3$ topological insulator thin films. In contrast to previous works using atomically flat cleaved bulk Bi$_2$Se$_3$ crystal surfaces we observe a strong influence of the high step-edge density (terrace width about 10~nm) on MBE-grown Bi$_2$Se$_3$ substrates, which significantly promotes the growth of coalescing FeSe domains with small tetragonal crystal distortion without compromising the underlying Bi$_2$Se$_3$ crystal structure.

中文翻译：

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台阶边缘辅助在外延 Bi$_2$Se$_3$ 薄膜上大规模 FeSe 单层生长

据报道，在与绝缘氧化物衬底的界面处，FeSe 的临界温度提高了一个数量级以上的单层极限后，人们对 Fe-硫属化物非常规超导体产生了浓厚的兴趣。在包含 FeSe 与拓扑绝缘体的界面的异质结构中，预计会出现其他有趣的物理现象，例如 {\it 拓扑超导} 的形式。迄今为止，Fe-硫族化物单层的超导特性主要通过局部扫描隧道光谱实验进行研究，该实验可以检测态密度中的赝间隙作为库珀配对的指标。由于难以生长具有均质材料特性的薄膜，因此很少报道可以证明或伪造超导相的直接宏观传输特性。在这里，我们报告了一种有前景的生长方法，可以在分子束外延生长的 Bi$_2$Se$_3$ 拓扑绝缘体薄膜上制造单层厚 FeSe 的连续地毯。与之前使用原子级平坦劈裂块体 Bi$_2$Se$_3$ 晶体表面的工作相比，我们观察到高阶跃边缘密度（梯形宽度约 10~nm）对 MBE 生长的 Bi$_2$Se$ 的强烈影响_3$ 衬底，这显着促进了具有小的四方晶体畸变的聚结 FeSe 域的生长，而不会损害潜在的 Bi$_2$Se$_3$ 晶体结构。