A combined first-principles calculations and X-ray photoelectron spectroscopy of Ce2T3X9 (T = Rh, Ru, Ir; X = Al, Ga): Possible strong topological insulator state in Ce2Ir3Al9

We calculated electronic structure of Ce2Rh3Ga9, Ce2Ru3Ga9, La2Ir3Al9 and Ce2Ir3Al9 compounds and we found that Ce2Ir3Al9 may exhibit strong topological insulator state according to Z2 index estimation based on parity algorithm and shape of band structure near Fermi level. The same algorithm shows strong topological insulator state for La2Ir3Al9 and Ce2Rh3Ga9 compounds, but their band structure near Fermi level is more like semimetallic one. Ce2Ru3Ga9 is a normal metal. Our calculations show no magnetic ordering for studied compounds. We also measured the XPS (X-ray Photoelectron Spectroscopy) spectra for these materials, and compared the valence band with simulated spectra, where good agreement was found. Core level states were also investigated and compared with Mulliken population analysis results. According to our measurements and calculations, the highest Ce valence is observed for Ce2Ir3Al9 whereas for Ce2Rh3Ga9 and Ce2Ru3Ga9 the Ce valence is smaller. Hybridization between conduction electrons and 4f states is very small, and for Ce2Ru3Ga9 essentially negligible.