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Kitamoto, Katsuyuki; Taguchi, Y.; Mimura, Koji; Ichikawa, K.; Aita, Osamu; Ishibashi, Hiroki

doi:10.1103/physrevb.68.195124

Cited by 11 publications

(6 citation statements)

References 17 publications

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“…The energy difference between these two excitations represents the splitting between the empty e g and t 2g states and is found to be about 2.8 eV. This splitting is also consistent with the DFT and cluster model calculation value of about 2.6 eV [22,23] .…”

supporting

confidence: 86%

X-ray-induced electronic structure change in CuIr2S4

et al. 2011

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The electronic structure of CuIr2S4 has been investigated using various bulk-sensitive x-ray spectroscopic methods near the Ir L3-edge: resonant inelastic x-ray scattering (RIXS), x-ray absorption spectroscopy in the partial fluorescence yield (PFY-XAS) mode, and resonant x-ray emission spectroscopy (RXES). A strong RIXS signal (0.75 eV) resulting from a charge-density-wave gap opening is observed below the metal-insulator transition temperature of 230 K. The resultant modification of electronic structure is consistent with the density functional theory prediction. In the spin-and charge-dimer disordered phase induced by x-ray irradiation below 50 K, we find that a broad peak around 0.4 eV appears in the RIXS spectrum.

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confidence: 86%

X-ray-induced electronic structure change in CuIr2S4

et al. 2011

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“…The beam was focused to a spot of 4 mm diameter. Figure 2 shows the Cu 2p spectrum of CuIr 2 S 4 taken at 300 K. The Cu 2p spectrum is similar to that reported previously [11,12,20]. The characteristic satellite structure, found in divalent Cu oxides such as CuO [21], is not observed in this spectrum.…”

supporting

confidence: 74%

X-Ray Photoemission Study ofCuIr2S4: Ir3+−Ir
Takubo
¹
,
Hirata
²
,
Son
³

et al. 2005
Phys. Rev. Lett.
46
3
33
1
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We have studied the electronic structure of the spinel-type compound CuIr 2 S 4 using x-ray photoemission spectroscopy (XPS). CuIr 2 S 4 undergoes a metal-insulator transition (MIT) at 226 K. In going from the metallic to insulating states, the valence-band photoemission spectrum shows a gap opening at the Fermi level and a rigid-band shift of 0:15 eV. In addition, the Ir 4f core-level spectrum is dramatically changed by the MIT. The Ir 4f line shape of the insulating state can be decomposed into two contributions, consistent with the charge disproportionation of Ir 3 :Ir 4 1:1. XPS measurements under laser irradiation indicate that the charge disproportionation of CuIr 2 S 4 is very robust against photoexcitation in contrast to Cs 2 Au 2 Br 6 which shows photo-induced valence transition.The spinel-type compound CuIr 2 S 4 has been attracting much interest because of its first-order metal-insulator transition (MIT) at T MI 226 K accompanied by the loss of localized magnetic moments [1][2][3][4][5][6]. Since the valence state of the Cu ion is Cu , an ionic configuration of Cu Ir 3 Ir 4 S 2ÿ 4 is expected in the insulating phase [7][8][9][10][11][12]. A recent structural study [13] indicates that the cubic spinel structure of CuIr 2 S 4 becomes tetragonally elongated along the c axis and that octamers of Ir 3 (S 0) and Ir 4 (S 1=2) are formed below T MI . In the Ir 4 octamer, the Ir 4 ions are dimerized in two directions (see Fig. 1). Croft et al. have found a dramatic electronic structural change above the Fermi level (E F ) across the MIT using x-ray absorption spectroscopy [4]. They have proposed that the low-temperature structure can be decomposed into onedimensional chains and that the dimerization due to charge and orbital ordering, i.e., the charge density wave formation along the chain direction, is responsible for the electronic structural change [4]. Very recently, it has been proposed that the dimerization in CuIr 2 S 4 and MgTi 2 O 4 [14] can be understood as an orbitally driven Peierls transition [15]. The experimental and theoretical studies indicate that the electronic structure of CuIr 2 S 4 itself is very exotic and interesting. Another interesting point is that the resistivity of CuIr 2 S 4 is dramatically reduced by x-ray or visible light irradiation in the insulating phase [16 -18]. It has been proposed that the photoexcitations break the Ir 3 =Ir 4 charge ordering and induce metallic conductivity.The nature of charge ordering and the effect of light irradiation are still controversial, partly because of the difficulty in the photoemission measurement. Photoemission spectroscopy is a powerful technique to investigate electronic states below E F although it is a surface sensitive method and clean surface must be prepared to obtain precise information. In previous photoemission studies of polycrystalline CuIr 2 S 4 , the Ir 4f core-level spectrum was reported to show no spectral change across the MIT [11,12] and no evidence of charge ordering was obtained. The Ir 4f photoemission data can provide ...

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“…The indication of MIT and the Ir 3+ /Ir 4+ charge ordering has been obtained on previous x-ray photoemission and absorption studies of CuIr 2 S 4 . [27,31,32,33,34,35] The Ir 4f core-level spectrum of the insulating phase has two components with large energy difference, consistent with the charge ordering of Ir sites. [27,35] In contrast, the core-level spectrum has not been changed against laser irradiation, while the resistivity is reduced.…”

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confidence: 76%

In-gap state and effect of light illumination inCuIr2S4probed by photoemission spectroscopy

et al. 2008

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We have studied disorder-induced in-gap states and effect of light illumination in the insulating phase of spinel-type CuIr 2 S 4 using ultraviolet photoemission spectroscopy ͑UPS͒. The Ir 3+ / Ir 4+ charge-ordered gap appears below the metal-insulator transition temperature. However, in the insulating phase, in-gap spectral features with softgap are observed in UPS just below the Fermi level ͑E F ͒, corresponding to the variable range hopping transport observed in resistivity. The spectral weight at E F is not increased by light illumination, indicating that the Ir 4+ -Ir 4+ dimer is very robust, although the long-range octamer order would be destructed by the photoexcitation. Present results suggest that the Ir 4+ -Ir 4+ bipolaronic hopping and disorder effects are responsible for the conductivity of CuIr 2 S 4 .

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Ir5dstate ofCuIr2S4:

Cited by 11 publications

References 17 publications

X-ray-induced electronic structure change in CuIr2S4

X-ray-induced electronic structure change in CuIr2S4

X-Ray Photoemission Study ofCuIr2S4: Ir3+−Ir
Takubo
¹
,
Hirata
²
,
Son
³

et al. 2005
Phys. Rev. Lett.
46
3
33
1
View full text Add to dashboard Cite

In-gap state and effect of light illumination inCuIr2S4probed by photoemission spectroscopy

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Ir5dstate ofCuIr2S4:

Cited by 11 publications

References 17 publications

X-ray-induced electronic structure change in CuIr2S4

X-ray-induced electronic structure change in CuIr2S4

X-Ray Photoemission Study ofCuIr2S4: Ir3+−IrTakubo1, Hirata2, Son3 et al. 2005Phys. Rev. Lett.463331View full textAdd to dashboardCite

In-gap state and effect of light illumination inCuIr2S4probed by photoemission spectroscopy

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X-Ray Photoemission Study ofCuIr2S4: Ir3+−Ir
Takubo
¹
,
Hirata
²
,
Son
³

et al. 2005
Phys. Rev. Lett.
46
3
33
1
View full text Add to dashboard Cite