Crystal Growth And Electronic Structure Of Hole-Doped Iridate Sr₃Ir₂O₇

Ruddlesden-Popper iridates,the 5d electron counterpart of cuprate high temperature superconductors,have attracted much attention due to the coexistence of crystal field interaction,spin orbit coupling and coulomb interaction.The systematic study of this material system is helpful to deepen the understanding of novel quantum phenomena in doped Mott insulators.The main contents of the thesis are as follows:（1）In order to achieve both high energy resolution and real space resolution in angle-resolved photoemission spectroscopy（ARPES）,we have developed an ultraviolet laser light-source with a tunable spot size.At present,the spot size can be tuned from 20-150 μm continuously,the laser power is continuously adjustable,and the spot position is precisely adjustable.（2）By doping hole carriers into Sr₃Ir₂O₇ system（e.g.substitution of Ir by Rh）,one can possibly study the metal insulator transition and associated exotic quantum phenomena.However,the Rh-doped Sr₃Ir₂O₇ bilayer structure is not very stable.Therefore,it is difficult to grow high quality single crystals with a high Rh doping level.Currently,the highest doping level reported in Rh-doped Sr₃Ir₂O₇ single crystals is only around 3%.We have systematically optimized the growth conditions,and obtained single crystals with high Rh doping level of 8-10%,which is beyond the highest doping level reported before.At the same time,the samples have been fully characterized,demonstrating the high quality of the single crystals.Transport measurements have further confirmed the existence of metal insulator transition in the high doping samples.（3）In order to understand the metal insulator transition in 5d transition metal oxides,it is necessary to investigate the effects of electron correlation and antiferromagnetic orders.Sr₃(Ir_1-xRh_x)₂O₇ is an ideal system to study this problem.By using ARPES,we have investigated the electronic structure of Sr₃(Ir_1-xRh_x)₂O₇.The results show an energy gap of about 20 meV at low temperature（T=30 K）.The gap closes at a temperature of around 100K.After exploring the magnetic properties,we have found that the gap closing temperature is consistent with the magnetic transition temperature（TN）in this system.Therefore,we speculate that the system would undergo a transition from Mott-insulator to Slater-insulator with Rh doping.The metal insulator transition in this system,which can be controlled by both chemical doping and temperature,would also enrich the phase diagram of quasi-two-dimensional d electron materials,and stimulate more future studies on the Ruddlesden-Popper iridium oxide Sr₃Ir₂O₇.