论文标题
欧盟掺杂拓扑绝缘子BI $ _2 $ te $ _3 $
Incipient antiferromagnetism in the Eu-doped topological insulator Bi$_2$Te$_3$
论文作者
论文摘要
稀土离子通常比过渡金属离子表现出更大的磁矩，因此有望在拓扑绝缘子的狄拉克表面状态下开放更大的交换间隙。然而，在最近对欧盟兴奋剂BI $ _2 $ te $ _3 $电影的光发作研究中，光谱保持无间隙至$ t = 20 \; \ text {k} $。在这里，我们仔细检查该系统中是否存在实质性差距形成的条件是否通过将光谱和批量表征方法与理论计算相结合。对于所有研究的欧盟掺杂浓度，我们对$ M_ {4,5} $ X射线吸收和磁性圆形二分法光谱的原子多重分析揭示了EU $^{2+} $ Valence，并确认了一个巨大的磁矩，与$ 4F^7 \ \; \; {^8} s_ {7/2} $接地状态。在低于$ 10 \; \ text {k} $的温度下，块状磁力测定指示反铁磁（AFM）排序的开始。这与密度功能理论非常吻合，该理论可以预测欧盟杂质之间的AFM相互作用。我们的结果支持以下观点：抗势力磁性可以与稀有地掺杂的bi $ _2 $ _3 $的拓扑表面状态共存，并在开尔文系列中呼吁进行光谱研究，以寻找新型的量子现象，例如量子异常霍尔效应。
Rare earth ions typically exhibit larger magnetic moments than transition metal ions and thus promise the opening of a wider exchange gap in the Dirac surface states of topological insulators. Yet, in a recent photoemission study of Eu-doped Bi$_2$Te$_3$ films, the spectra remained gapless down to $T = 20\;\text{K}$. Here, we scrutinize whether the conditions for a substantial gap formation in this system are present by combining spectroscopic and bulk characterization methods with theoretical calculations. For all studied Eu doping concentrations, our atomic multiplet analysis of the $M_{4,5}$ x-ray absorption and magnetic circular dichroism spectra reveals a Eu$^{2+}$ valence and confirms a large magnetic moment, consistent with a $4f^7 \; {^8}S_{7/2}$ ground state. At temperatures below $10\;\text{K}$, bulk magnetometry indicates the onset of antiferromagnetic (AFM) ordering. This is in good agreement with density functional theory, which predicts AFM interactions between the Eu impurities. Our results support the notion that antiferromagnetism can coexist with topological surface states in rare-earth doped Bi$_2$Te$_3$ and call for spectroscopic studies in the kelvin range to look for novel quantum phenomena such as the quantum anomalous Hall effect.
