Searching For Majorana Fermion In Artificial Topological Superconductor

Majorana fermion is an exotic particle,whose anti-particle is exactly the same with itself.In condensed matter,Majorana fermion exists as a quasi-particle excitation in topological su-perconductors.It obeys non-Abelian statistics and thus can be used in fault-tolerant topological quantum computation,which greatly enhances the application ability of quantum computer.No topological superconductor in nature has been confirmed yet.Physicists however built a heterostructure of superconductor and topological insulator.In the heterostructure,the topolog-ical surface states acquire the superconductivity from the superconducting substrate via proxim-ity effect and become topological superconductor.Applied magnetic field,Majorana fermion will existed in the excited vortex core on the surface of the heterostructure.There exist two major difficulties in the research of Majorana fermion in artificial topo-logical superconductor.One is to find proper materials for the heterostructure.The other is to detect the Majorana fermion.In 2012,the group in SJTU successfully grown epitaxial topo-logical insulator Bi₂Se₃ films on top of superconductor NbSe2 which built a milestone of in this research.In the following years,they built the heterostructure Bi₂Te₃/NbSe₂and detected Majorana fermions in such system via STM.Majorana fermion is an electronic state the lies at zero energy.In the vortex core,there exist other low energy states that is unrepeatable under current STM energy resolution.This is the major hinder in the detection of Majorana fermion.However,researchers found that the spatial distribution of Majorana fermion is significantly different from other excitation states in the vortex core.By carefully analysis the spatial distribution of the excitation states in the vortex core of the heterostructure,they found solid evidences of the existence of Majorana fermion for the first time.In this thesis,we found new evidence of the existence of Majorana fermion in that system.We found MZM in the vortex core has spin-selective Andreev reflection process.We detected the spin property of the MZM via a spin-polarized STM experimentally for the first time.This result is not only another solid evidence of the existence of Majorana fermion,but also provided a new approach for detecting Majorana fermion,and moreover,raise a potential manipulating approach of the MZM that may contribute to quantum computation.We also searched other artificial topological superconductor such as ultra-thin Bi film on NbSe₂.We systematically analyzed the growing process of the Bi film on the substrate.We found the coexistence of topological edge states and superconductivity on Bi?111?bilayer.This result suggests a new kind of artificial topological superconductor.In the last part of the thesis,we researched in the epitaxial growth of potential topolog-ical superconductor Fe_1+yTe_0.5Se_0.5on graphene.We studied the growth mode of different compounds in this three elements material and sucessfully made FeTe_xSe_1-x on the surface of graphene.