Estyunina Tatiana P, Shikin Alexander M, Estyunin Dmitry A, Eryzhenkov Alexander V, Klimovskikh Ilya I, Bokai Kirill A, Golyashov Vladimir A, Kokh Konstantin A, Tereshchenko Oleg E, Kumar Shiv, Shimada Kenya, Tarasov Artem V
Department of Physics, Saint Petersburg State University, St. Petersburg 198504, Russia.
Donostia International Physics Center, 20018 Donostia-San Sebastián, Spain.
Nanomaterials (Basel). 2023 Jul 24;13(14):2151. doi: 10.3390/nano13142151.
One of the approaches to manipulate MnBi2Te4 properties is the magnetic dilution, which inevitably affects the interplay of magnetism and band topology in the system. In this work, we carried out angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations for analysing changes in the electronic structure of Mn1-xGexBi2Te4 that occur under parameter x variation. We consider two ways of Mn/Ge substitution: (i) bulk doping of the whole system; (ii) surface doping of the first septuple layer. For the case (i), the experimental results reveal a decrease in the value of the bulk band gap, which should be reversed by an increase when the Ge concentration reaches a certain value. Ab-initio calculations show that at Ge concentrations above 50%, there is an absence of the bulk band inversion of the Te pz and Bi pz contributions at the Γ-point with significant spatial redistribution of the states at the band gap edges into the bulk, suggesting topological phase transition in the system. For case (ii) of the vertical heterostructure Mn1-xGexBi2Te4/MnBi2Te4, it was shown that an increase of Ge concentration in the first septuple layer leads to effective modulation of the Dirac gap in the absence of significant topological surface states of spatial redistribution. The results obtained indicate that surface doping compares favorably compared to bulk doping as a method for the Dirac gap value modulation.
调控MnBi2Te4性质的方法之一是磁稀释，这不可避免地会影响该体系中磁性与能带拓扑结构之间的相互作用。在这项工作中，我们进行了角分辨光电子能谱（ARPES）测量和密度泛函理论（DFT）计算，以分析在参数x变化时Mn1-xGexBi2Te4电子结构的变化。我们考虑了两种Mn/Ge替代方式：（i）整个体系的体掺杂；（ii）第一层七重层的表面掺杂。对于情况（i），实验结果表明体带隙值减小，当Ge浓度达到一定值时，这种减小应该会反转。从头算计算表明，在Ge浓度高于50%时，Γ点处Te pz和Bi pz贡献的体带反转消失，带隙边缘的态在空间上有显著的重新分布进入体相，这表明体系中发生了拓扑相变。对于垂直异质结构Mn1-xGexBi2Te4/MnBi2Te4的情况（ii），结果表明在第一层七重层中增加Ge浓度会导致在没有显著空间重新分布的拓扑表面态的情况下有效调制狄拉克隙。所获得的结果表明，作为一种调制狄拉克隙值的方法，表面掺杂比体掺杂更具优势。
