Molecular Beam Epitaxy Growth And Scanning Tunneling Microscopy Studies Of PdTe₂/Bi₂Te₃ Heterostructures

Majorana fermions?MFs?,their own antiparticle,obey non-Abelian statistics,which have attracted huge interest for their potential applications in topological quantum computing.MFs are predicted to exist in topological superconductors?TSCs?,but natural TSCs are very rare.Fortunately,some theoretical physicists predicted that the heterostructures composed of s-wave superconductors?SC?and three-dimensional strong topological insulators?TI?are ideal platforms for detecting MFs.Following this prediction,the existence of Majorana fermions has been experimentally confirmed in several TI/s-wave SC heterostructures.Heterostructures are constructed by depositing TI films on the SC substrate surface,thereby allowing the direct observation of the spatial distribution of MFs on the TI surface.However,in order to manipulate Majorana fermions,SC should be deposited on top of TI.PdTe₂ bulk is a transition-metal dichalcogenide,which exhibits exotic properties,such as superconductivity?Tc¹.7 K?,topological surface state,and type-II Dirac fermions.Moreover,PdTe₂ thin film also exhibits superconductivity;therefore,PdTe₂ is an ideal candidate for a SC to be fabricated on TI.In this thesis,we study the growth conditions of PdTe₂films on TI.The surface topography and electronic properties of PdTe₂/Bi₂Te₃ heterostructures were investigated through in situ scanning tunneling microscopy/spectroscopy?STM/STS?,and the superconductivity of the samples was measured using ex situ two-coil mutual inductance technique.The main results in this thesis are listed below:?1?High quality PdTe₂ films with different thicknesses were successfully grown on Bi₂Te₃ under Te-rich conditions.Using STM,we studied the topographies of the PdTe₂/Bi₂Te₃ heterostructures.STM images of PdTe₂ films clearly exhibited the atomically flat surface and small random height modulation.The measured step height and in-plane lattice constant of PdTe₂ are about 0.51nm and 0.40 nm,which are consistent with the value of bulk PdTe₂.?2?At low coverage of PdTe₂,the Bi₂Te₃ regions uncovered by PdTe₂were studied by STM.The defect density of Bi₂Te₃ surface is very low,which indicates that the Pd atoms prefer to form PdTe₂ films.Moreover,the electronic properties of PdTe₂/Bi₂Te₃ heterostructures were investigated by STS.The measurements show that PdTe₂ films exhibit an electron donor behavior,causing a 40-meV downshift of the Dirac point of Bi₂Te₃.?3?By means of applying the ex suit two-coil mutual inductance technique,the superconductivity of the PdTe₂/Bi₂Te₃ heterostructure with a transition temperature of about 1.4 K was observed.However,the superconductivity of the uncovered Bi₂Te₃ needs to be further investigated.