Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

19B/2003G008

Soft x-ray emission from valence band to S 2p in CuIr2S4
Yukihiro TAGUCHI*, Katsuyuki Kitamoto, Kojiro MIMURA, Tatsunori NODA, Yukihiro FUJITA,
Kouichi ICHIKAWA, Osamu AITA, Hiroki ISHIBASHI
Osaka Prefecture Univ., Gakuencho, Nakaku, Sakai, Osaka 599-8531, Japan
Thiospinel CuIr2S4 exhibits simultaneous structural,
metal-to-insulator (MI) and paramagnetic-to-diamagnetictransitions around 230 K with decreasing temperature.
The formal Ir valency is 3.5+. It has been considered thatcharge ordering (CO) of Ir ions takes place in theinsulating phase of CuIr2S4 [1]. The CO of Ir ions inCuIr2S4 may partly result from electron correlation amongIr 5d electrons. Such effect has been suggested by the factthat the valence-band (VB) structure of CuIr2S4 obtainedby photoemission spectroscopy (PES) disagrees withband-structure calculations with respect to Ir 5d-derived
structure despite qualitative agreement for Cu 3d- and S
3p-derived features [2,3]. It is considered that theelectronic states near the Fermi level EF or the VB
maximum plays an important role in the MI and COtransitions of CuIr2S4. According to the band-structure
calculations the states near EF are mainly ascribed to Ir
5d-S 3p hybridized band [2]. In this work we haveinvestigated the S 3p states hybridized with Ir 5d in
CuIr2S4 by means of soft x-ray emission spectroscopy(XES). When a sulfur 2p core-hole is created, radiativetransitions from VB to S 2p reflect the S 3p hybridized
with nd and/or ns orbitals because of the dipole selection
rule for XES and of the localized nature of the core hole.
10Cu ion of CuIr2S4 has essentially a 3d configuration [3].
Measurements were carried out at beamline BL-19B.
The sample used was a sintered poly-crystal. The sample
surface was cleaned in situ by scraping.
Fig. 1 shows the S L2,3 XES spectrum of CuIr2S4 at 275
K (open circles). EF corresponds to the S 2p1/2 binding

Fig.1. S L2,3 soft x-ray emission spectrum of CuIr2S4 at275 K (open circles). Broken, dotted and solid lines aredecomposed L2 and L3 emission spectra and the sum ofthem, respectively.

energy of CuIr2S4 determined by PES. A shoulder
structure in XES is seen at 0.8 eV below EF in agreementwith the previous PES measurement (dots in Fig. 2). A
previous PES study has revealed that the structure has
contribution from Ir 5d [4]. Thus the structure in XES
results from the S 3p-Ir 5d hybridized band in accord withthe band-structure calculations. In order to confirm that
the S 2p spin-orbit splitting of ~1.2 eV does not cause thestructure, we decomposed the S L2,3 spectrum of CuIr2S4
into L2 (2p1/2) and L3 (2p3/2) spectra. We assumed that thetransition probability from VB to S 2p1/2 and 2p3/2 depends
only on the statistical weight of each core state, i.e.
intensity ratio of 2:1 and that each spectrum can be
reproduced by superposition of several Voigt functions.
The obtained L2 and L3 spectra are also shown in Fig. 1.
The S L2 XES, PES and theoretical spectra are comparedin Fig. 2. The S L2 spectrum shows that the S 3p stateshybridized with Ir 5d are distributed over almost theentire energy region of VB in good agreement with S 3p
partial density of states obtained by the band-structure
calculations [2].
References[1] T. Furubayashi et al., J. Phys. Soc. Jpn. 63, 3333
(1994), S. Nagata et al., Phys. Rev. B 58, 6844 (1998),
P. G. Radaelli, Nature 416, 155 (2002).
[2] T. Oda et al., J. Phys.: Condens. Matter 7, 4433 (1995).
[3] J. Matsuno et al., Phys. Rev. B 55, R15979 (1997).
[4] K. Kitamoto et al., Physica B, to be published.
* taguchi@ms.osakafu-u.ac.jp

Fig. 2. Comparison of S L2 x-ray emission (solid line)with photoemission (dots) and theoretical spectra (brokenline) given in Ref. 3.

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