The Fe-based superconductor Fe (Se,Te) combines non-trivial topology with unconventional superconductivity and may be an ideal platform to realize exotic states such as high-order topological corner modes and Majorana modes. Thin films of Fe (Se,Te) are particularly important for device fabrication and phase sensitive transport measurements. While bulk Fe (Se,Te) has been extensively studied, the nature of the superconducting order parameter in the monolayer limit has not yet been explored. In this work, we study monolayer films of Fe (Se,Te) on Bi₂Te₃ with scanning tunneling spectroscopy. Monolayer Fe (Se,Te)/Bi₂Te₃ heterostructures host a multigap superconducting state that strongly resembles the bulk. Analysis of the phase-referenced quasiparticle interference signal reveals a sign-changing s-wave order parameter similar to the bulk as well as a unique pattern of sign changes which have not been observed in the bulk. Our work establishes monolayer Fe (Se,Te)/Bi₂Te₃ as a robust multi-band unconventional superconductor and sets the stage for explorations of non-trivial topology in this highly-tunable system.

铁基超导体Fe(Se,Te)结合了非平凡拓扑和非常规超导性，可能是实现高阶拓扑角模和马约拉纳模等奇异态的理想平台。Fe (Se,Te) 薄膜对于器件制造和相敏传输测量尤为重要。虽然大量 Fe (Se,Te) 已被广泛研究，但尚未探索单层极限超导有序参数的性质。在这项工作中，我们使用扫描隧道光谱研究了 Bi ₂ Te ₃上的 Fe (Se,Te) 单层膜。单层 Fe (Se,Te)/Bi ₂ Te ₃异质结构具有与本体非常相似的多间隙超导状态。对相位参考准粒子干涉信号的分析揭示了一个与块体相似的符号变化 s 波阶数参数，以及在块体中未观察到的独特符号变化模式。我们的工作建立了单层 Fe (Se,Te)/Bi ₂ Te ₃作为稳健的多频带非常规超导体，并为探索这个高度可调系统中的非平凡拓扑奠定了基础。