title: Origin of Pressure-induced Superconducting Phase in KxFe2-ySe2 studied by Synchrotron X-ray Diffraction and Spectroscopy.
abstract: Pressure dependence of the electronic and crystal structures of KxFe2-ySe2, which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change of Fermi surface topology. Our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.
authors: Graduate School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan.
authors: Yoshiya
authors: Y
authors: Yamamoto
authors: RIKEN SPring-8 Center, RIKEN, 1-1-1 Kouto, Mikazuki, Sayo, Hyogo 679-5148, Japan.
authors: Hitoshi
authors: H
authors: Yamaoka
authors: MANA, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
authors: Masashi
authors: M
authors: Tanaka
authors: MANA, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.|Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai, Miyagi 980-8577, Japan.
authors: Hiroyuki
authors: H
authors: Okazaki
authors: Graduate School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan.|MANA, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
authors: Toshinori
authors: T
authors: Ozaki
authors: MANA, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
authors: Yoshihiko
authors: Y
authors: Takano
authors: Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA.|Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai 201203, China.
authors: Jung-Fu
authors: JF
authors: Lin
authors: Center for Science and Technology under Extreme Conditions (KYOKUGEN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors: Hidenori
authors: H
authors: Fujita
authors: Center for Science and Technology under Extreme Conditions (KYOKUGEN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors: Tomoko
authors: T
authors: Kagayama
authors: Center for Science and Technology under Extreme Conditions (KYOKUGEN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors: Katsuya
authors: K
authors: Shimizu
authors: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors: Nozomu
authors: N
authors: Hiraoka
authors: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors: Hirofumi
authors: H
authors: Ishii
authors: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors: Yen-Fa
authors: YF
authors: Liao
authors: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors: Ku-Ding
authors: KD
authors: Tsuei
authors: Graduate School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan.
authors: Jun'ichiro
authors: J
authors: Mizuki