Phys. Rev. Research 3, 023075 (2021)

Evidence for a percolative Mott insulator-metal transition in doped Sr₂IrO₄

Zhixiang Sun^1,2,*, Jose M. Guevara², Steffen Sykora^2,3, Ekaterina M. Pärschke⁴, Kaustuv Manna^2,5, Andrey Maljuk², Sabine Wurmehl^2,6, Jeroen van den Brink², Bernd Büchner^2,6,7, and Christian Hess^2,7,8,†

1 Center for Joint Quantum Studies and Department of Physics, Tianjin University, 300072 Tianjin, China

2 Leibniz-Institute for Solid State and Materials Research, IFW-Dresden, 01069 Dresden, Germany

3 Institute for Theoretical Physics, TU Dresden, 01069 Dresden, Germany

4 Department of Physics, University of Alabama at Birmingham, Alabama 35294, USA

5 Max-Planck-Institute for Chemical Physics of Solids, 01187 Dresden, Germany

6 Institute for Solid State Physics, TU Dresden, 01069 Dresden, Germany

7 Center for Transport and Devices, TU Dresden, 01069 Dresden, Germany

8 Fakultät für Mathematik und Naturwissenschaften, Bergische Universität Wuppertal, 42097 Wuppertal, Germany

*  zsun@tju.edu.cn

†  c.hess@uni-wuppertal.de

ABSTRACT

Despite many efforts to rationalize the strongly correlated electronic ground states in doped Mott insulators, the nature of the doping-induced insulator-to-metal transition is still a subject under intensive investigation. Here, we probe the nanoscale electronic structure of the Mott insulator Sr₂IrO_4−δ with low-temperature scanning tunneling microscopy and find an enhanced local density of states (LDOS) inside the Mott gap at the location of individual defects which we interpret as defects at apical oxygen sites. A chiral behavior in the topography for those defects has been observed. We also visualize the local enhanced conductance arising from the overlapping of defect states which induces finite LDOS inside of the Mott gap. By combining these findings with the typical spatial extension of isolated defects of about 2 nm, our results indicate that the insulator-to-metal transition in Sr₂IrO_4−δ could be percolative in nature.