Investigations Of Majorana Zero Mode In Iron-based Superconductor FeTe_0.55Se_0.45

With the development of the society,people are faced with more and more huge and complex information,which puts forward higher requirements for computing capacity and speed of computer.For this reason,the design of quantum computer came into being.Despite the huge computing capacity and ultrahigh speed,quantum computer has to face the problem that it is easy to cause operation errors due to the disturbance of environment.The topological quantum computer,based on Majorana zero mode(MZM),has fault-tolerant property due to the protection of topological property of system.Thus,the search for Majorana zero mode in condensed matter has been one of the most fascinating research area.In this dissertation,Majorana zero mode(MZM)in vortex core and on the Fe adatoms on the surface of FeTe_0.55Se_0.45 is studied by an extremely low temperature high magnetic fields Ultra-high vacuum STM-MBE joint system.In addition,the electronic properties of novel two dimensional(2D)material Pd₂Se₃ are also investigated.The main works and novelty are listed below:1.MZM in vortex core on the surface of FeTe_0.55Se_0.45 single crystal was detected.MZM does not shift and split when cross the vortex.Its decay is consistent to Fu-Kane model.The full width at half maximum(FWHM)is close to the energy resolution at0.55 K.MZM disappears at 3 K because of the thermal excitation in the bulk.The results provide strong evidences for the existence of MZM.Compared with other system,we can detect MZM in single material without construct complex junction.The measurement temperature is enhanced to liquid helium temperature region.FeTe_0.55Se_0.45 has provide a new platform for the research and application of MZMs.2.MZM at Fe adatom on the surface of FeTe_0.55Se_0.45 was also observed.Fe atoms were deposited on the surface of FeTe_0.55Se_0.45 and a robust zero-bias peak(ZBP)coexisted with bound states with integer level-spacing was observed on Fe adatoms.The characteristics of ZBP under different temperature and magnetic field are similar to MZM in the field-induced vortex.The adsorbed position of Fe atoms is changed by STM tip.It is observed that there is a close relationship between the emergence of MZM and the adsorbed site.The reversible transition between YSR states and MZM is also observed by changing the exchange coupling through varying tip-sample distance.In addition,the fusion of MZMs in QAV and field-induced vortex is also observed.MZM can emerge at Fe adatoms on the surface of FeTe_0.55Se_0.45 without applying a magnetic field,which provide a more flexible platform to study and manipulate MZMs.3.The electronic properties of 2D material Pd₂Se₃ was studied by STM/S.The band gap of monolayer Pd₂Se₃ is about 1.23 e V.A p-type band bending on the step edge of bilayer Pd₂Se₃ is observed.An in-plain lattice deformation is observed and the band gap near the deformation shows n-type band bending.In addition,the Se-vacancy defect level near valence band is highly anisotropic.This work lays the foundation for the future construction of devices and applications based on Pd₂Se₃.