Surface Conductivity Of The Honeycomb Spin-Orbit Mott Insulator Na2iro3

The search for materials with novel and unusual electronic properties is at the heart of condensed matter physics as well as the basis to develop conceptual new technologies. In this context, the correlated honeycomb transition metal oxides have attracted large attention for both, being a possible experimental realization of the theoretically predicted magnetic Kitaev exchange and the theoretical prospect of topological nontriviality. Mott-insulating Na2IrO3 is prototypical among these materials, characterized by crystal field splitting, spin-orbit coupling, and Hubbard repulsion being on similar energy scales. Herein, a combined electrical transport and scanning tunneling spectroscopy (STS) study of the surface of sodium iridate cleaved and in situ investigated under ultrahigh vacuum is reported. Temperature-dependent transport measurements prove the existence of surface conductance with a surprisingly high and temperature-independent conductivity. STS shows a variety of different spectra. Most importantly, a significant density of states is found within the bandgap of sodium iridate at the surface. Based on the local spectroscopic information, multiple conductive channels with differing nature being simultaneously apparent in this material are discussed.