Superconducting Proximity Effect In Topological Insulator BiSbTeSe₂

Recently,Majorana fermion has attracted increasing attention.Its antiparticle is itself and obeys non-abelian statistics,which can be used to build quantum computer protected by topology.In condensed matter physics,Majorana zero modes existing at the boundary of topological superconductor has been theoretically predicted.Although there still lacks of a common agreement that intrinsic topological superconductor has been identified,it has been found that the combination of s-wave superconductor and topological insulator may yield topological superconductor like superconductivity via proximity effect.The content of this thesis is related to this issue.In this thesis,the physical properties of three-dimensional topological insulators are characterized,superconducting proximity effect on three-dimensional topological insulators is studied,and a series of measurements are carried out.We characterize the properties of quaternary topological insulators at low temperature and in strong magnetic field.Hall-bar devices were fabricated by micro-nano processing,the magnetoresistance and Hall resistance of the material were measured,and the carrier concentration and mobility of the material were obtained.Next,we prepared a series of superconducting quantum interferometers on three-dimensional topological insulators,and found that the quality of the interface between the superconducting electrode and the topological insulator has a great influence on the superconducting proximity effect.The interface can be improved by plasma bombardment.A detailed study on this issue were carried out.Finally,we fabricated devices with good superconducting proximity effect,and observed a clear supercurrent-phase relation.To further study its topological properties,we fabricated asymmetrical superconducting quantum interference devices withAl/Al₂ O₃/Al as the large junction and the one based on topological insulator as the small junction.In order to eliminate the quasi-particle poisoning effect,we performed pulse measurement to explore the distribution of the switch current,and applied magnetic field to change the phase to explore the supercurrent-phase relation,and some peculiar bimodal distributions were observed.To better study the topological properties,the next step is to highlight the topological signals by improving the quality of materials and using high-frequency measurements,laying a foundation for future work.