title: Role of valence fluctuations in the superconductivity of Ce122 compounds.
abstract: Pressure dependence of the Ce valence in CeCu(2)Ge(2) has been measured up to 24 GPa at 300 K and to 17 GPa at 18-20 K using x-ray absorption spectroscopy in the partial fluorescence yield. A smooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in Ce(Cu(1-x)Ni(x))(2)Si(2) at 20 K. A very weak, monotonic increase of the valence with x was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results show no evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.
authors.affiliation: RIKEN SPring-8 Center, Sayo, Hyogo 679-5148, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Yamaoka
authors.affiliation: Department of Physics, Okayama University, Okayama 700-8530, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Ikeda
authors.affiliation: National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: I
authors.initials: I
authors.lastname: Jarrige
authors.affiliation: Quantum Beam Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Tsujii
authors.affiliation: Graduate School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Zekko
authors.affiliation: Graduate School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Graduate School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Mizuki
authors.affiliation: Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA and Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai 201203, China.
authors.forename: J-F
authors.initials: JF
authors.lastname: Lin
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors.forename: N
authors.initials: N
authors.lastname: Hiraoka
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors.forename: H
authors.initials: H
authors.lastname: Ishii
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors.forename: K-D
authors.initials: KD
authors.lastname: Tsuei
authors.affiliation: Department of Physics, Okayama University, Okayama 700-8530, Japan.
authors.forename: T C
authors.initials: TC
authors.lastname: Kobayashi
authors.affiliation: Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan.
authors.forename: F
authors.initials: F
authors.lastname: Honda
authors.affiliation: Faculty of Science, Ryukyu University, Nakagami, Okinawa 903-0213, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Onuki