Electronic properties of topological materials and NMR

拓扑材料的电子性质和核磁共振

• 批准号: 442459148
• 负责人: Professor Dr. Jürgen Haase
• 金额: --
• 依托单位: Felix-Bloch-Institut für Festkörperphysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/442459148?language=en
• 关键词: Electronic; properties; topological; materials; NMR

Recently, with nuclear magnetic resonance (NMR) experiments we discovered unexpected signatures of the special electronic properties of topological materials. For example, the energy band inversion, responsible for the topological properties, affects the local charge symmetry, and for an inversion at the zone center it results in a NMR quadrupole splitting that we found to be in quantitative agreement with first principle calculations. Less well understood is the observation of a magnetic field induced change of the local charge symmetry, which can lead to orientation independent quadrupole effects if the crystal is rotated in a magnetic field - never reported with NMR experiments before. It is stipulated that electrons in total angular momentum states in these strongly spin-orbit coupled systems can follow the magnetic field direction to some extent, an effect that is known only in atomic physics. The life time of the involved electronic states must lead to a new nuclear relaxation mechanisms, of electric quadrupolar and magnetic dipolar origins. Finally, we found a strong indirect inter-nuclear coupling in these materials. While not unexpected for small bandgap systems, recent theory is only in qualitative agreement with experiment. But this mechanism will be vital for the behavior of magnetic impurities studied by many groups.We propose to investigate these effects in greater detail for a number of topological materials. This includes Bi2Se3 with various conduction electron densities, as well as the closely related systems Bi2Te3, Bi2Te2Se, Sb2Te3, and Bi(1.08)Sb(0.9)Sn(0.02)Te2S. Then, systems with more complex, non-trivial band topology from the Bi(x)Te(M) family (x=1,2,3, M= I, Br) will be studied. Collaboration with theory groups will advance our understanding of these new effects.

最近，我们通过核磁共振（NMR）实验发现了拓扑材料特殊电子性质的意外特征。例如，能带反转，负责的拓扑性质，影响当地的电荷对称性，并在区域中心的反转，它会导致NMR四极分裂，我们发现是在定量协议与第一原理计算。不太清楚的是观察到磁场引起的局部电荷对称性的变化，如果晶体在磁场中旋转，这可能导致取向独立的四极效应-以前从未报道过NMR实验。在这些强自旋轨道耦合系统中，处于总角动量态的电子可以在一定程度上跟随磁场方向，这种效应只有在原子物理学中才知道。所涉及的电子状态的寿命必须导致一个新的核弛豫机制，电四极和磁偶极的起源。最后，我们发现在这些材料中有很强的间接核间耦合。虽然对于小带隙系统并不意外，但最近的理论仅与实验定性一致。但是，这种机制将是至关重要的磁性杂质的行为研究的许多团体。我们建议调查这些影响更详细的一些拓扑材料。这包括具有各种传导电子密度的Bi 2Se 3，以及密切相关的系统Bi 2 Te 3，Bi 2 Te 2Se，Sb 2 Te 3和Bi（1.08）Sb（0.9）Sn（0.02）Te 2S。然后，我们将研究Bi（x）Te（M）族（x= 1，2，3，M= I，Br）中具有更复杂的非平凡能带拓扑的系统。与理论小组的合作将促进我们对这些新效应的理解。