Scanning tunneling microscopy and spectroscopy on Kondo insulators

近藤绝缘体的扫描隧道显微镜和光谱学

• 批准号: 314808123
• 负责人: Dr. Steffen Wirth
• 金额: --
• 依托单位: Max-Planck-Institut für Chemische Physik fester Stoffe (MPI CPfS)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/314808123?language=en
• 关键词: Scanning; tunneling; microscopy; spectroscopy; Kondo

The theoretically predicted existence of topologically protected surface states in the so-called Kondo insulators still awaits clear-cut experimental verification. Even in case of the heavily studied material SmB6, there are conflicting experimental results. In order to advance, we will focus our efforts on investigating the exact nature of the in-gap states in SmB6 using scanning tunneling microscopy and spectroscopy to lower temperatures and in magnetic field. STM investigations up to now exist only for the (001) surface. However, due to the polar nature of this surface several complications arise. We will, therefore, extend our investigations also to (110) and (111) surfaces, on which Dirac points protected by crystal symmetry are predicted to be present. The effects of magnetic and non-magnetic impurities on the surface states will be explored by using La and Gd substituted materials as well as by in situ deposition of magnetic and non-magnetic impurities using an e-beam evaporator on cleaved surfaces of SmB6. The outcome of these investigations will be compared to theoretical predictions. Our studies will also include other candidate Kondo insulators, e.g. Ce3Bi4Pt3, CeNiSn and CeOs4Sb12. If the topologically non-trivial nature of the surface states can be established several device applications are conceivable. Through collaborations within the SPP1666 complementary spectroscopic methods, such as angle-resolved photoelectron spectroscopy (ARPES), Raman spectroscopy, other optical spectroscopies, and measurements of surface transport using a multi-probe STM will be utilized to study the in-gap states. In addition, theoretical input will be obtained via collaborations with SPP1666 participants. These will include calculations based on density functional theory and dynamical mean field theory (DFT + DMFT) as well as calculations of tunneling spectra and quasiparticle interference patterns. Through such concerted efforts we hope to achieve deepened insight into the physics of Kondo insulators and the nature of its surface states.

所谓的近藤绝缘体中存在拓扑保护表面态的理论预测仍有待明确的实验验证。即使在对材料SmB6进行了大量研究的情况下，也有相互矛盾的实验结果。为了取得进展，我们将集中精力利用扫描隧道显微镜和光谱来研究SmB6中带隙内态的确切性质，以降低温度和在磁场中进行。到目前为止，STM研究仅限于(001)面。然而，由于这个表面的极地性质，出现了几个复杂的问题。因此，我们还将把我们的研究扩展到(110)和(111)表面，在这些表面上，预计存在受晶体对称性保护的狄拉克点。利用La和Gd替代材料以及利用电子束蒸发器在SmB6解理表面原位沉积磁性和非磁性杂质，将探索磁性和非磁性杂质对表面态的影响。这些调查的结果将与理论预测进行比较。我们的研究还将包括其他候选近藤绝缘体，如Ce3Bi4Pt3、CeNiSn3和CeOs4Sb12。如果表面态在拓扑上的非平凡性质能够被确立，那么几种器件的应用是可以想象的。通过SPP1666内部的合作，将利用角度分辨光电子能谱(ARPES)、拉曼光谱、其他光学光谱以及使用多探针扫描隧道显微镜测量表面传输等互补光谱方法来研究带隙内状态。此外，理论投入将通过与SPP1666参与者的合作获得。这些将包括基于密度泛函理论和动力学平均场理论(DFT+DMFT)的计算，以及隧道谱和准粒子干涉图样的计算。通过这样的共同努力，我们希望对近藤绝缘体的物理及其表面态的性质有更深入的了解。