Scanning Tunneling Microscopy Study Of Strongly Correlated Iridates

New quantum ground states have received increasing attention in recent years.It has been recognized that spin-orbit coupling can lead to non-trivial band topology in weakly interacting electronic systems,such as topological insulators and semimetals,but the importance of electron-electron interaction in strongly spin-orbit coupling systems has not been totally understood.It is new materials with remarkable electron correlation and strong spin-orbit coupling can make this kind of study possible.Most of these materials belong to4d or 5d transition metal compounds,especially in iridates or Ir-based salts.In this thesis,we have systematically studied two kinds of iridates,including Ga-doping Sr₂IrO₄ with metal-insulator phase transition and Na₂IrO₃ with honeycomb structure.The main conclusions are as follows:1.Conducting channels in Sr₂IrO₄ with 5%Ga dopingThe cleaved plane of Sr₂IrO₄ with 5%Ga doping shows obvious inhomogeneity.The further results show that the inhomogeneity is induced by the variation of spatial local density of states because of Ga doping,and the differential conductance through the doping region shows a transition from U-shaped gap to V-shaped gap,that is,metal-insulator transition.Finally,in the differential conductance maps,the conducting channels are observed.2.Crystalline structure and properties of zigzag Ir-O-Ir bond in Na₂IrO₃An energy gap of 420 me V is observed at 77 K for Na₂IrO₃ single crystal,which confirms that Na₂IrO₃is a Mott insulator,not a Slater insulator.Thermal annealing can not only tune the content of Na atoms on the sample surface,but also change the energy gap.Finally,the tip modified by oxygen atom can obtain ultra-high resolution topography.The anisotropic zigzag Ir-O-Ir bond may be related to the zigzag antiferromagnetic order due to strong spin-orbit coupling.