Study On Low Temperature Transport Of Topological Insulator Bi₂Te₃

Quantum Hall effect opens the door to the field of condensed matter topology.The introduction of Chen number and the proposal of Haldane model make people begin to explore the meaning of topology in physics.With the further understanding,more conventional topological materials are proposed and found.Topological insulators protected by time inversion symmetry are deeply studied,and then more topological classifications are proposed.The branch of topology in condensed matter is developing more and more widely.Topological edge states have unique properties.On this basis,people propose a scheme to construct Majorana quasiparticles.Because the latter’s Non-Abelian statistical rules can be used to construct topological qubits,it has become a hot research topic in physics in recent ten years.The Kitaev model of one-dimensional system has a profound inspiration.The scheme of constructing Majorana quasiparticles in strong spin orbit coupled nanowires derived from this model is the one that has achieved the most results.The three-dimensional topological insulator surface proximitized by superconductor proposed by Fu and Kane to realizes p-wave like superconductivity,used to constructs Josephson junction,and Majorana quasiparticles by adjusting the superconducting electrode’s phase,is also a very important scheme.It has the advantages of easy regulation and expansion.Based on this scheme,I have carried out the following research work.In Part One,the superconducting proximity between superconducting electrode and three-dimensional topological insulator is studied.In the Fu Kane’s model,the premise of realizing the Majorana quasiparticle is to effectively adjacent the superconductor on the surface of the topological insulator.The nature of the adjacent superconductor further determines the construction of the Majorana quasiparticle.Therefore,it is very necessary to understand the physical process.Through transport measurements,I found that there are two unconventional superconducting behaviors in the common system Al/Ti/Bi₂Te₃:the enhancement of superconducting gap and critical magnetic field with the magnetic field.By means of VSM,TEM and EDX,I found that Ti and Bi₂Te₃ will produce magnetic substances,which will lead to the superconducting energy gap first increase and then decrease with the magnetic field.Why the enhanced critical magnetic field appears needs further research.In Part Two,I study the realization of Majorana quasiparticles by using anomalous phase to modulate Josephson junction.How to control the phase of Josephson junction is a key problem.For the first time,I use the abnormal phase caused by spin orbit coupling and Zeeman field to construct Majorana quasiparticles.The"right-angle junction"is designed to independently regulate the phase of half junction region.The interference pattern with theπphase of half junction region and 0 is of another half is obtained through numerical simulation,which is in good agreement with the experimental data,indicating that the phase of half junction region has been modulated toπ,which lays a foundation for finding Majorana quasiparticles at the corner in the next step.I also found the semi-integer Shapiro steps of right-angle junction through microwave measurement,which may come from the coexistence of 0-πjunction or forward leaning current phase relationship.In Part Three,the FFLO phenomenon in topological insulator SQUID is studied.Due to the unique properties of the surface state of topological insulator,unconventional superconducting pairing is easy to appear after being adjacent to superconductivity.In addition to p-wave like superconductivity,FFLO superconductivity with non-zero net momentum may also appear.In the transport measurement,I found the evidence that the superconducting order parameter oscillates in two directions,which is consistent with the simulated image,implying the existence of FFLO superconducting state.The above three works further explore the implementation scheme of Fu-Kane model,deepen the understanding of the superconducting proximity of topological insulators,and lay a foundation for the construction of topological qubits.