Figure 1: Characterization of (001) cleaved Sr₂IrO₄surface.

(a), A ball model of the crystal structure of Sr₂IrO₄. (b), A typical topographic image of the (001) surface. The setup conditions for imaging were a sample-bias voltage of 50 mV and a tunneling current of 0.1 nA. The surface was created by cleavage between two SrO layers without breaking IrO₆ octahedra. The right panel shows a cross-section along the line in the left panel. (c), Atomically resolved image shows a square lattice of Sr atoms. (d), A typical LEED image at the cleaved (001) surfaces of Sr₂IrO₄ measured at room temperature. LEED pattern shows 1 × 1 and √2 × √2 fractional spots (marked by arrows). (e), Averaged tunneling spectrum taken at 80 K, showing the opening insulating gap (averaged over an area of 100 nm × 100 nm by a grid spectroscopic mode with 20 × 20 sampling pixels). Data were taken with a sample bias voltage of −50 mV and a tunneling current of 0.1 nA. Bias-modulation amplitude was set to 3 mV_rms.