fig1

Figure 1. STM topographic images and the tunneling spectrum of the cleaved Na₂IrO₃ surface. (A) The representative STM topographic image of the RT-cleaved surface of Na₂IrO₃ (V_b = +1.5 V, I_t = 20 pA, image size: 30 × 30 nm²). The inset shows the corresponding crystalline structure of Na₂IrO₃. The Na, O and Ir atoms are represented with blue, red and pink balls, respectively. (B) The upper panel shows the highly resolved STM images of two types of surface defects, assigned as Na and O vacancies, respectively. The corresponding simulated images of Na and O vacancies are provided in the lower panel, and their bias voltages are V_b = +2.0 and -1.9 V, respectively. (C) dI/dV curves measured at the pristine surface and the site of the O vacancy, respectively (T = 77 K). Both spectra possess a uniform fully opened gap. The gap width is 420 meV. STS spectra were acquired using a lock-in technique with AC modulation of 15 mV.