Studies On The Topological Properties Of Sr_xBi₂Se₃ And (Pb_0.5Sn_0.5)_0.7In_0.3Te

The greatest triumph of condensed matter physics in 20th century is the classifi-cation of quantum states by the band theory and the principle of spontaneous symme-try breaking.However,with the discovery of the quantum Hall state,this paradigm showed its incompleteness.In order to achieve a full understanding of the quantum phase transition in quantum Hall states,the concept of topological order was intro-duced into condensed matter physics.After numerous studies,it is now well-known that the topological theory can be applied to any condensed matter systems with a full energy gap,such as insulators and superconductors.The topological theory has great-ly enriched the physical intension of the band theory.Topological insulators(TIs)are topological nontrivial phases,and have topologically protected surface states which is called Dirac cone.Topological superconductors(TSCs)are the novel superconductors that have nontrivial topological order.TSC exhibits the topologically protected in-gap states on surface which are known as the Majorana states.In particular,each vortex in two dimensional TSC can trap one Majorana quasiparticle.Such kind of quasiparticle obeys non-Abelian statistics and thus has potential application to topological quantum computation and quantum information storage.The exploration on TSC will deep-en people's understanding of condensed matter physics,and has considerable realistic significance.This thesis mainly shows the experimental researches on serval possible three dimensional TSCs and heterostructures constructed with topological insulator thin film.The text contains 5 issues as listed below:1,The scanning tunneling spectroscopy measurements of the surface density of s-tates(DOS)of In-doped topological crystalline insulator Pb0.5Sn0.5Te.The results show the contradiction with the theoretical predictions for a bulk TSC,and we conclude that(Pb0.5Sn0.5)0.7In0.3Te is not a TSC.2,The systematic scanning tunneling microscopy/spectroscopy study of the possi-ble TSC SrxBi2Se3.The results show SrxBi2Se3 has full superconducting gap without any in-gap DOS as expected theoretically for a bulk TSC.More importantly,we find that the surface Dirac electrons within the bulk superconducting gap will simultaneous-ly condense into the superconducting state.This vividly demonstrates how the surface Dirac electrons are driven into Cooper pairs.3,The measurement of the c-axis resistivity of SrxBi2Se3 by using a Corbino-shape like electrode configuration,with the magnetic field rotating within the basal planes.The results provide clear evidence of two-fold superconductivity which is con-sistent with the theoretical prediction.This research strongly suggests that SrxBi2Se3 is a TSC.4,The discovery of merging the two important components:Dirac electrons and the correlation effect in heterostructured Bi2Te3/Fe1+?Te by molecular beam epitaxy method.We observed the gapped feature of the DOS of Dirac electrons at the Fermi energy due to the correlation effect of Fe1+?Te.5,The construction of topological insulator(Bi2Te3)/superconductor(FeTe1-xSex)heterostructre by molecular beam epitaxy method,and the observation of the proximity effect induced superconducting gap on the Bi2Te3 film.This experiment provides a good platform for the following research of two dimensional TSC and the Majorana quasiparticle.