Quasiparticles and Charge Transfer At the Two Surfaces of the Honeycomb Iridate \( \mathrm{Na_2 IrO_3} \)

L. Moreschini, I. Lo Vecchio, Nicholas P. Breznay, S. Moser, S. Ulstrup, R. Koch, J. Wirjo, C. Jozwiak, K. S. Kim, E. Rotenberg, A. Bostwick, J. G. Analytis, and A. Lanzara

Physical Review B 96 (2017) 161116

Abstract

Direct experimental investigations of the low-energy electronic structure of the \( \mathrm{Na_2 IrO_3} \) iridate insulator are sparse and draw two conflicting pictures. One relies on flat bands and a clear gap, the other involves dispersive states approaching the Fermi level, pointing to surface metallicity. Here, by a combination of angle-resolved photoemission, photoemission electron microscopy, and x-ray absorption, we show that the correct picture is more complex and involves an anomalous band, arising from charge transfer from Na atoms to Ir-derived states. Bulk quasiparticles do exist, but in one of the two possible surface terminations the charge transfer is smaller and they remain elusive.

* denotes faculty author.

† denotes student author.