马约拉纳零能模的自旋极化扫描隧道谱研究

Majorona zero modes hosted in topological superconductors can mimic Majorana fermions whose particles are their own anti-particles. They are distinguished by their novel non-Abelian statistics property and tantalizing prosperity of applications in topological quantum computations. Previous studies have detected the existing evidence of Majorana fermions based on a proposed scheme of constructing effective topological superconductors via proximity induced superconductivity in topological surface states. However, the evidences still lack further experimental confirmation. In this project, we will measure the theoretically expected real space spin textures associated with Majorana zero modes with Cr tips whose spin direction is invariant against moderate magnetic fields. These includes the systematic investigations of the spin-dependent local density of states around the vortex cores of Bi2Te3/NbSe2 heterostructures and the intrinsic topological superconductor FeTe0.55Se0.45, which will provide vital evidences to the Majorana zero modes in those two systems. Moreover, we will also grow high quality FeTe0.55Se0.45 samples with molecular beam epitaxy to improve the inhomogenities of Se and Te ratio in bulk samples, which is highly desirable for further research and applications. Our study will deepen our understanding towards the spin properties of Majorana zero modes and add a new dimension to the spin-sensitive measurement technique in the study of new material systems.

拓扑超导体中的马约纳拉零能模可以模拟反粒子是其本身的马约纳拉费米子，并具有新奇的非阿贝尔统计性质和拓扑量子计算应用前景。前期工作基于拓扑表面态的超导紧邻效应构筑有效拓扑超导体的方案，已经发现磁通涡旋处马约纳拉零能模存在的证据，但是仍然需要进一步检验。本项目将利用自旋极化扫描隧道显微镜在实空间探测理论上预期存在的与马约纳拉零能模相关的实空间自旋构形。这包括利用抗一定外磁场影响的Cr针尖，系统研究Bi2Te3/NbSe2异质结体系和本征拓扑超导体FeTe0.55Se0.45体系中磁通涡旋处的实空间自旋态密度性质，为马约纳拉零能模提供更为确凿的检验证据。另外，还将通过分子束外延生长FeTe0.55Se0.45薄膜样品，改善现有体样品材料中的不均匀性，为其进一步的研究和应用奠定材料基础。本项目的实施将加深对马约纳拉零能模自旋特性的理解，并推动自旋极化探测技术在新材料体系中的应用发展。

关联作用导致的新奇量子现象是凝聚态物理研究的核心问题之一。本项目计划研究强自旋轨道耦合与超导关联作用导致的拓扑超导体中的马约纳拉零能模的自旋极化属性。针对该项目研究内容，我们发展了自旋极化扫描隧道显微镜实验技术和利用分子束外延制备具有关联效应的薄膜体系，针对拓扑超导体样品中存在不均匀性的问题及时调整了研究途径，发现了一系列新奇的关联物态。主要成果包括：（1）二维极限下CrTe2薄膜的磁序转变和Fe4Se5薄膜的强反铁磁序。（2）纯一维电荷密度波态中的新型相子-极化子准粒子激发。（3）二维极限下1T-NbSe2的莫特绝缘体相。（4）单电子转移控制的Hubbard型库伦阻塞效应与单自旋YSR态。（5）二维极限下的铁电和反铁电序与可控相变。（6）利用维度效应调控拓扑半金属Na3Bi到二维拓扑绝缘体的拓扑相变。（7）通过原子插层方法在双层FeSe2中构建人工笼目晶格。本项目的研究对人工构筑低维量子体系，揭示新型关联效应提供了重要平台。