Single surface state at a strongly correlated electronic structure in Na$_{2}$IrO$_{3}$: a candidate d-electron topological insulator

We have performed angle-resolved photoemission spectroscopy (ARPES) on Na$_{2}$IrO$_{3}$, a 5d transition metal oxide (TMO) which is a strong insulator with a honeycomb lattice structure and has been theoretically proposed as a candidate for a new class of topological insulators (TIs). The near E$_{F}$ electronic structure of Na$_{2}$IrO$_{3}$ was carefully mapped, which shows an overall agreement to the first-principle calculations with spin-orbit (SO) coupling and electron correlation (U), though certain discrepancy remains. Specifically, we found an extra electron-like pocket near the Fermi level with Dirac-cone-like dispersion around $\Gamma $ point. The further photon energy dependent studies show no k$_{z}$-dispersion of this electron-like pocket, and the metal deposition studies show a great enhancement and sharpening of this feature. These results confirm its surface state nature and suggest a possible single topological surface state at the Brillouin zone (BZ) center in Na$_{2}$IrO$_{3}$.