Browsing by Author "Altendorf, S. G."

Now showing 1 - 2 of 2

Charge-transfer energy in iridates: A hard x-ray photoelectron spectroscopy study
(2020-07-13)
Takegami, D.
;
Kasinathan, D.
;
Wolff, K. K.
;
Altendorf, S. G.
;
Chang, C. F.
We have investigated the electronic structure of iridates in the double perovskite crystal structure containing either Ir4+ or Ir5+ using hard x-ray photoelectron spectroscopy. The experimental valence band spectra can be well reproduced using tight-binding calculations including only the Ir 5d, O 2p, and O 2s orbitals with parameters based on the downfolding of the density-functional band structure results. We found that, regardless of the A and B cations, the A(2)BIrO(6) iridates have essentially zero O 2p to Ir 5d charge-transfer energies. Hence double perovskite iridates turn out to be extremely covalent systems with the consequence being that the magnetic exchange interactions become very long ranged, thereby hampering the materialization of the long-sought Kitaev physics. Nevertheless, it still would be possible to realize a spin-liquid system using the iridates with a proper tuning of the various competing exchange interactions.
Molecular beam epitaxy preparation and in situ characterization of FeTe thin films
(2020-02-28)
Pereira, V. M.
;
Wu, C. N.
;
Liu, C. E.
;
Liao, S-S
;
Chang, C. F.
We have synthesized Fe1+y Te thin films by means of molecular beam epitaxy (MBE) under Te-limited growth conditions. We found that epitaxial layer-by-layer growth is possible for a wide range of excess Fe values, wider than expected from what is known from studies on the bulk material. Using x-ray magnetic circular dichroism spectroscopy at the Fe L-2(,3) and Te M-4(,5) edges, we observed that films with high excess Fe contain ferromagnetic clusters while films with lower excess Fe remain nonmagnetic. Moreover, x-ray absorption spectroscopy showed that it is possible to obtain films with very similar electronic structure as that of a high quality bulk single crystal Fe-1.(14) Te. Our results suggest that MBE with Te-limited growth may provide an opportunity to synthesize FeTe films with smaller amounts of excess Fe as to come closer to a possible superconducting phase.