Browsing by Author "Liao, Y. F."

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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.
Distribution of electronic reconstruction at the n-type LaAlO(3)/SrTiO(3) interface revealed by hard x-ray photoemission spectroscopy
(2011-12-26)
Chu, Y. Y.
;
Liao, Y. F.
;
Tra, V. T.
;
Yang, J. C.
;
Liu, W. Z.
We investigated the electronic reconstruction at the n-type LaAlO(3)/SrTiO(3) interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti(4+) to Ti(3+) occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO(3) with a depth of about 48 angstrom (similar to 12 unit cells) and an estimated total charge transfer of similar to 0.24 electrons per two-dimensional unit cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672099]
Distribution of electronic reconstruction at the n-type LaAlO3/SrTiO3 interface revealed by hard x-ray photoemission spectroscopy
(2011-12-26)
Chu, Y. Y.
;
Liao, Y. F.
;
Tra, V. T.
;
Yang, J. C.
;
Liu, W. Z.
We investigated the electronic reconstruction at the n-type LaAlO3/SrTiO3 interface with hard x-ray photoelectron spectroscopy (HAXPES) under grazing incidence. By exploiting the collapse of evanescent x-ray waves and the abrupt increase of x-ray absorption at the critical incidence angle, our HAXPES study reveals a 2% electronic reconstruction from Ti4+ to Ti3+ occurring near the interface. Such an electronic reconstruction also extends from the interface into SrTiO3 with a depth of about 48 angstrom (similar to 12 unit cells) and an estimated total charge transfer of similar to 0.24 electrons per two-dimensional unit cell. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672099]
Electronic structure investigation of a charge density wave coupled to a metal-to-metal transition in Ce3Co4Sn13
(2018-12-18)
Singh, A.
;
Huang, H. Y.
;
Chin, Y. Y.
;
Liao, Y. F.
;
Huang, T. C.
We study the electronic structure of the skutterudite Ce3Co4Sn13, which is known to exhibit a charge density wave (CDW) transition, at temperature T-CDW similar to 160 K, coupled to a metal-to-metal transition. We use temperature dependent hard x-ray photoemission spectroscopy (HAXPES) and x-ray absorption spectroscopy (XAS) to investigate the occupied and unoccupied electronic states of Ce3Co4Sn13. The Co 2p and Sn 3p core level spectra show small but finite shifts in binding energy positions across T-CDW while Ce 3d core level spectra do not show any change across the transition. The Ce M-4,M-5-edge XAS spectrum compared with calculations indicate a typical trivalent ionic Ce3+ spectral shape, ruling out Kondo screening in Ce3Co4Sn13. In contrast, the Co L-2,L-3-edge XAS spectrum compared with a calculated spectrum shows evidence for hybridization with neighboring Sn atoms in a trigonal prismatic co-ordination. Temperature dependent XAS across the Co L-2,L-3-edge shows a small shift across T-CDW, consistent with HAXPES results. Detailed XAS measurements as a function of temperature show that the spectral shifts occur with a hysteresis across T-CDW , indicative of a first-order transition. Valence band spectra show a normal Fermi edge above and below T-CDW. The Co 3d states are observed at a binding energy of similar to 2 eV while the Ce 4f states occur as a weak feature within 0.5 eV of the Fermi level. The results suggest an unusual CDW transition coupled to a metal-to-metal transition in Ce3Co4Sn13.