Two-dimensional (2D) topological materials, including quantum spin/anomalous Hall insulators, have attracted intense research efforts owing to their promise for applications ranging from low-power electronics and high-performance thermoelectrics to fault-tolerant quantum computation. One key challenge is to fabricate topological materials with a large energy gap for room-temperature use. Stanene—the tin counterpart of graphene—is a promising material candidate distinguished by its tunable topological states and sizeable bandgap. Recent experiments have successfully fabricated stanene, but none of them have yet observed topological states. Here we demonstrate the growth of high-quality stanene on Cu(111) by low-temperature molecular beam epitaxy. Importantly, we discovered an unusually ultraflat stanene showing an in-plane s–p band inversion together with a spin–orbit-coupling-induced topological gap (~0.3 eV) at the Γ point, which represents a foremost group-IV ultraflat graphene-like material displaying topological features in experiment. The finding of ultraflat stanene opens opportunities for exploring two-dimensional topological physics and device applications.

二维（2D）拓扑材料，包括量子自旋/异常霍尔绝缘体，由于其在从低功率电子学和高性能热电学到容错量子计算等应用的希望，已引起了广泛的研究努力。一个关键的挑战是制造在室温下具有大能隙的拓扑材料。石墨烯的锡替代物Stanene是一种很有前途的材料候选者，以其可调的拓扑状态和较大的带隙而著称。最近的实验已经成功地制备了锡，但还没有观察到拓扑状态。在这里，我们证明了低温分子束外延在Cu（111）上生长高质量的stanene。重要的是，我们发现了一种不寻常的超扁平锡烯，显示出平面内s–p波段反转以及自旋轨道耦合在Γ点引起的拓扑间隙（〜0.3 eV），代表了在实验中显示出拓扑特征的IV类超平石墨烯类材料。超扁平锡的发现为探索二维拓扑物理和设备应用打开了机会。