title: How Cooper pairs vanish approaching the Mott insulator in Bi2Sr2CaCu2O8+delta.
abstract: The antiferromagnetic ground state of copper oxide Mott insulators is achieved by localizing an electron at each copper atom in real space (r-space). Removing a small fraction of these electrons (hole doping) transforms this system into a superconducting fluid of delocalized Cooper pairs in momentum space (k-space). During this transformation, two distinctive classes of electronic excitations appear. At high energies, the mysterious 'pseudogap' excitations are found, whereas, at lower energies, Bogoliubov quasi-particles-the excitations resulting from the breaking of Cooper pairs-should exist. To explore this transformation, and to identify the two excitation types, we have imaged the electronic structure of Bi(2)Sr(2)CaCu(2)O(8+delta) in r-space and k-space simultaneously. We find that although the low-energy excitations are indeed Bogoliubov quasi-particles, they occupy only a restricted region of k-space that shrinks rapidly with diminishing hole density. Concomitantly, spectral weight is transferred to higher energy r-space states that lack the characteristics of excitations from delocalized Cooper pairs. Instead, these states break translational and rotational symmetries locally at the atomic scale in an energy-independent way. We demonstrate that these unusual r-space excitations are, in fact, the pseudogap states. Thus, as the Mott insulating state is approached by decreasing the hole density, the delocalized Cooper pairs vanish from k-space, to be replaced by locally translational- and rotational-symmetry-breaking pseudogap states in r-space.
authors.affiliation: LASSP, Department of Physics, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Kohsaka
authors.forename: C
authors.initials: C
authors.lastname: Taylor
authors.forename: P
authors.initials: P
authors.lastname: Wahl
authors.forename: A
authors.initials: A
authors.lastname: Schmidt
authors.forename: Jhinhwan
authors.initials: J
authors.lastname: Lee
authors.forename: K
authors.initials: K
authors.lastname: Fujita
authors.forename: J W
authors.initials: JW
authors.lastname: Alldredge
authors.forename: K
authors.initials: K
authors.lastname: McElroy
authors.forename: Jinho
authors.initials: J
authors.lastname: Lee
authors.forename: H
authors.initials: H
authors.lastname: Eisaki
authors.forename: S
authors.initials: S
authors.lastname: Uchida
authors.forename: D-H
authors.initials: DH
authors.lastname: Lee
authors.forename: J C
authors.initials: JC
authors.lastname: Davis