title: Coexistence of Fermi arcs and Fermi pockets in a high-T(c) copper oxide superconductor.
abstract: In the pseudogap state of the high-transition-temperature (high-T(c)) copper oxide superconductors, angle-resolved photoemission (ARPES) measurements have seen Fermi arcs-that is, open-ended gapless sections in the large Fermi surface-rather than a closed loop expected of an ordinary metal. This is all the more puzzling because Fermi pockets (small closed Fermi surface features) have been suggested by recent quantum oscillation measurements. The Fermi arcs cannot be understood in terms of existing theories, although there is a solution in the form of conventional Fermi surface pockets associated with competing order, but with a back side that is for detailed reasons invisible to photoemission probes. Here we report ARPES measurements of Bi(2)Sr(2-x)La(x)CuO(6+delta) (La-Bi2201) that reveal Fermi pockets. The charge carriers in the pockets are holes, and the pockets show an unusual dependence on doping: they exist in underdoped but not overdoped samples. A surprise is that these Fermi pockets appear to coexist with the Fermi arcs. This coexistence has not been expected theoretically.
authors.affiliation: National Laboratory for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Jianqiao
authors.initials: J
authors.lastname: Meng
authors.forename: Guodong
authors.initials: G
authors.lastname: Liu
authors.forename: Wentao
authors.initials: W
authors.lastname: Zhang
authors.forename: Lin
authors.initials: L
authors.lastname: Zhao
authors.forename: Haiyun
authors.initials: H
authors.lastname: Liu
authors.forename: Xiaowen
authors.initials: X
authors.lastname: Jia
authors.forename: Daixiang
authors.initials: D
authors.lastname: Mu
authors.forename: Shanyu
authors.initials: S
authors.lastname: Liu
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Dong
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Lu
authors.forename: Guiling
authors.initials: G
authors.lastname: Wang
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhou
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhu
authors.forename: Xiaoyang
authors.initials: X
authors.lastname: Wang
authors.forename: Zuyan
authors.initials: Z
authors.lastname: Xu
authors.forename: Chuangtian
authors.initials: C
authors.lastname: Chen
authors.forename: X J
authors.initials: XJ
authors.lastname: Zhou