稀土表面掺杂剂介导的拓扑绝缘体中磁致翘曲转变的实验演示
Experimental demonstration of a magnetically induced warping transition in a topological insulator mediated by rare-earth surface dopants
AI总结：
本研究通过在Bi₂Se₂Te表面沉积磁性稀土元素，实验观测到拓扑表面态的翘曲形状转变及带隙开启，验证了相关理论预测，为调控磁相互作用、实现量子反常霍尔效应提供了新路径。
摘要：
磁性拓扑绝缘体（MTI）是一类新型材料，其拓扑受保护的能带结构与长程铁磁序共存，这会导致时间反演对称性（TRS）破缺，在狄拉克锥形状的拓扑表面态（TSS）中引入带隙。此前已有预测，MTI中的带隙开启会伴随TSS的畸变，使其翘曲形状从六边形演变为三角形。在本研究中，我们在三元三维原型拓扑绝缘体Bi₂Se₂Te表面沉积低浓度的磁性稀土元素（即Er和Dy）后，通过角分辨光电子能谱演示了这种转变。我们还观测到了由TRS破缺导致的带隙开启特征，而上述转变的观测结果也佐证了该带隙的存在。此外，增加Er的覆盖度可实现TSS的可调p型掺杂。由此，我们的Bi₂Se₂Te晶体的费米能级（E_F）可被逐渐调向TSS的狄拉克点，进而调向磁致带隙，从而满足了在该体系中实现量子反常霍尔效应（QAHE）的两个必要前提条件。我们通过在调控TSS能带色散的哈密顿量中引入面外磁塞曼项的理论模型，对实验结果进行了解释。我们的研究结果提供了基于简单方法调控TSS磁相互作用的新策略，并为实现QAHE开辟了可行路径。
英文摘要：
Magnetic topological insulators (MTI) constitute a novel class of materials where the topologically protected band structure coexists with long-range ferromagnetic order, which can lead to the breaking of time-reversal symmetry (TRS), introducing a bandgap in the Dirac cone-shaped topological surface state (TSS). The gap opening in MITs has been predicted to be accompanied by a distortion in the TSS, evolving its warped shape from hexagonal to trigonal. In this work, we demonstrate such a transition by means of angle-resolved photoemission spectroscopy after the deposition of low concentrations of magnetic rare earths, namely Er and Dy, on the ternary three-dimensional prototypical topological insulator Bi$_2$Se$_2$Te. Signatures of the gap opening occurring as a consequence of the TRS breaking have also been observed, whose existence is supported by the observation of the aforementioned transition. Moreover, increasing the Er coverage results in a tunable p-type doping of the TSS. As a consequence, the Fermi level (E$_{\textrm{F}}$) of our Bi$_2$Se$_2$Te crystals can be gradually tuned towards the TSS Dirac point, and therefore to the magnetically induced bandgap; thus fulfilling two of the necessary prerequisites for the realization of the quantum anomalous Hall effect (QAHE) in this system. The experimental results are rationalized by a theoretical model where a magnetic Zeeman out-of-plane term is introduced in the hamiltonian governing the TSS band dispersion. Our results offer new strategies to control magnetic interactions with TSSs based on a simple approach and open up viable routes for the realization of the QAHE.
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