Two-dimensional (2D) superconductors that reside on substrates must be influenced by Rashba spin–orbit coupling (SOC). The intriguing effect of Rashba-type SOCs on iron-based superconductors (IBSs) has remained largely a mystery. In this work, we unveil modified Landau-level spectroscopy and the intricate band splitting of FeSe monolayers through the precision of scanning tunneling spectroscopy, which unequivocally demonstrates the presence of Rashba SOC. The discovery sheds light on a nonparabolic electron band at the X and/orY point, displaying a distinctive Landau quantization behavior characterized by E_n ∝ (nB)^4/3. The theoretical model aligns with our experimental insights, positing that the k⁴-term of the electron band becomes predominant and profoundly reshapes the band structure. Our results underscore the pivotal role of the Rashba SOC effect on 2D superconductors and set the stage to probe new quantum states in systems with remarkably low carrier concentrations.

中文翻译：

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通过扫描隧道光谱揭示 FeSe 单层的朗道级量子化和带分裂


位于衬底上的二维 （2D） 超导体必须受到 Rashba 自旋-轨道耦合 （SOC） 的影响。Rashba 型 SOC 对铁基超导体 （IBS） 的有趣影响在很大程度上仍然是一个谜。在这项工作中，我们通过扫描隧道光谱的精度揭示了改进的朗道级光谱和 FeSe 单层的复杂能带分裂，这明确证明了 Rashba SOC 的存在。这一发现揭示了 X 和/或 Y 点的非抛物线电子带，显示出以 E_n ∝ （nB）^4/3 为特征的独特朗道量子化行为。该理论模型与我们的实验见解一致，假设电子带的 k⁴ 项变得占主导地位，并深刻地重塑了能带结构。我们的结果强调了 Rashba SOC 效应对 2D 超导体的关键作用，并为在载流子浓度非常低的系统中探测新的量子态奠定了基础。