Optimizing interfaces between topological insulators and superconductors: Towards a local detection of Majorana states

该项目旨在制备拓扑绝缘体（TI）和s波超导体（SC）之间的界面，这些超导体在涡流中具有可检测的强大Majorana激发（ME）。这一目标面临三大挑战。首先，TI的狄拉克点能量艾德必须相当精确地处于费米能级EF，以降低涡旋内的平凡受限态的密度，从而增加保护ME的小间隙。在第一个项目阶段，我们已经建立了两种方法来调整艾德EF，无论是通过调整化学计量或通过生长的p-n结的可变厚度。其次，ME信号必须从SC的Caroli-de Gennes-Matricon状态中解脱出来。我们的方法是去除涡旋中的SC，或者更准确地说，将涡旋钉扎在s波SC的孔中。这具有额外的Vantage，即多个通量量子可以被孔捕获，使得ME签名在偶数个通量量子的情况下消失。为了实现这一目标，我们已经建立了一个超高真空（UHV）掩模对准，转移掩模结构的基板与100纳米的精度。第三，必须通过扫描隧道光谱（STS）来检测ME签名。为此，我们已经建立了STS低至370 mK的超高真空和B-场的能量分辨率为0.1 meV和电压噪声低于0.02 mV，从而提供了所需的属性检测ME。除了这些成就，我们追求的优先计划内的讨论产生的项目，即我们证实了预测的弱TI性能的Bi 14 Rh 3 I9（第一个实验实现的弱TI）通过探测其拓扑保护的边缘状态，同时，确定BiTe作为第二个弱TI。在第二个资金周期内，我们首先着眼于从FeSe开始沉积足够的SC，如果在SrTiO 3（110 K）或BaTiO 3（70 K）上沉积单层或在适当掺杂（50 K）后沉积多层，则FeSe已显示出异常的临界温度。然而，由于先验并不清楚，如果FeSe在BiSbTeSe合金上超导，我们可能会回到更传统的超导体NbSe 2，Nb或Pb。其次，我们将准备的孔结构，使用掩模对准在超高真空独立的SC的优化。最后得到的结构将详细探讨STS变化的B-场，温度，局部化学势，相邻的孔之间的距离，并可能，材料组合。注意，掩模对准器技术也可以被转移到弱TI，其应当在邻近感生边缘状态的结束处托管ME。

The project aims at the preparation of interfaces between topological insulators (TIs) and s-wave superconductors (SCs) hosting detectable, robust Majorana excitations (MEs) within vortices. This aim faces three major challenges. Firstly, the Dirac point energy ED of the TI has to be rather exactly at the Fermi level EF in order to reduce the density of trivially confined states within the vortex and, thus, to increase the minigap which protects the MEs. In the first project phase, we have established two methods to tune ED to EF, either by adapting the stoichiometry or by growing a p-n junction of variable thickness. Secondly, the ME signal must be disentangled from the Caroli-de Gennes-Matricon states of the SC. Our approach is to remove the SC within the vortices or, more precisely, to pin the vortices within holes of the s-wave SC. This has the additional ad¬vantage that multiple flux quanta can be caught by the holes such that the ME signature disappears in case of an even number of flux quanta. Towards that goal, we have established an ultrahigh-vacuum (UHV) mask aligner, which transfers mask structures to a substrate with 100 nm precision. Thirdly, the ME signatures have to be detected by scanning tunneling spectroscopy (STS). To this end, we have established STS down to 370 mK in UHV and B-field with an energy resolution of 0.1 meV and a voltage noise below 0.02 mV, thus, providing the required properties for the detection of MEs. Besides these achievements, we pursued a project resulting from discussions within the priority programme, namely we confirmed the predicted weak TI properties of Bi14Rh3I9 (first experimental realization of a weak TI) by probing its topologically protected edge states and, meanwhile, identified BiTe as a second weak TI. Within the second funding period, we firstly aim at the deposition of an adequate SC starting with FeSe, which has been shown to exhibit exceptional critical temperatures, if deposited as a monolayer on SrTiO3 (110 K) or BaTiO3 (70 K) or as a multilayer after adequate doping (50 K). However, since it is not clear a priori, if FeSe gets superconducting on BiSbTeSe alloys, we might get back to more conventional superconductors as NbSe2, Nb or Pb. Secondly, we will prepare the hole structure using mask alignment in UHV independently from the optimization of the SC. Finally the resulting structures will be probed in detail by STS varying B-field, temperature, the local chemical potential, the distance between adjacent holes, and, possibly, the materials combination. Note that the mask aligner technique can also be transferred to weak TIs, which should host MEs at the end of a proximity induced edge state.