Preparation Of Layered5d Iridates Ba₂IrO₄ Films And Modulation Of Transport Properties

In recent years,the 5d iridates have attracted great interest due to the interplay between spin-orbit coupling and Coulomb interactions that can give rise to novel quantum states.Iridates is an important system for exploring new high-temperature superconductors,which exhibits many properties similar to superconducting cuprates,including layered perovskite crystal structure,antiferromagnetic ground state,Fermi arc and V-shaped energy gap.In this paper,we improved the flux stability greatly by improving the design of the Ba source crucible in the molecular beam epitaxy?MBE?system,and discussed how to prepare high quality Ba₂Ir O₄ films in detail.Besides,the transport properties of Ba₂Ir O₄ films were tuned by many methods,including field-effect transistor?FET?,ionic liquid electric double layer transistor?EDLT?,lithium ion intercalation and epitaxy strain.The specific work and achievements are summarized as follows:1)Design of crucible with stable flux for Ba sourceThe change of the source surface morphology will have a great impact on the flux stability during the film growth process.By setting a detachable flux limiting device to ensure the stable saturated vapor pressure in the crucible.Here,using Ba as a test source,the improved crucible was applied to the growth of Ba₂Ir O₄ films,which successfully eliminated the influence of the source surface morphology change on the flux rate.So the flux rate depends on the stable and controllable crucible temperature,which greatly improves the flux stability of the source in MBE for a long time.2)Growth ofO4 film by MBEIn this paper,we optimized the growth parameter and prepared a series of Ba₂Ir O₄films under different eptixial strain by MBE.XRD shows that Ba₂Ir O₄ films grown on different substrates have high lattice quality.In addition,it is found that Ba₂Ir O₄ films has a high requirement for preservation environment.Therefore,we grow Sr Ti O₃capping layer in situ to protect Ba₂Ir O₄ film effectively,which creates the possibility to modulate the transport properties of Ba₂Ir O₄ film with different methods.3)Modulation of transport properties ofO4 filmThe transport properties of Ba₂Ir O₄ films were explored by doping high concentration and high uniformity carriers on Ba₂Ir O₄ films or lattice strain,including:1)introduce high concentration carriers into Ba₂Ir O₄ films by FET and ionic liquid EDLT;2)introduce carriers by lithium ion intercalation;3)grow Ba₂Ir O₄ films on different substrates to research the influence of lattice strain on its transport properties.Combined with theoretical calculation,the results show that with the increase of biaxial in-plane compression strain,both the overlap of Ba₂Ir O₄ electron orbit and the band width at Fermi surface increases,which leads to the decrease of resistance.The lattice strain can modulate the electronic structure of Ba₂Ir O₄ effectively.Our study provides the research basis and theoretical support for further study of potential novel quantum phenomena in Ba₂Ir O₄.