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How Cooper pairs vanish approaching the Mott insulator in Bi 2Sr2CaCu2O8+δ

Cornell Affiliated Author(s)

Author

Y. Kohsaka
C. Taylor
P. Wahl
A. Schmidt
J. Lee
K. Fujita
J.W. Alldredge
K. McElroy
J. Lee
H. Eisaki
S. Uchida
D.-H. Lee
J.C. Davis

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 Bi2Sr2CaCu 2O8+δ 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. ©2008 Macmillan Publishers Limited. All rights reserved.

Date Published

Journal

Nature

Volume

454

Issue

7208

Number of Pages

1072-1078,

URL

https://www.scopus.com/inward/record.uri?eid=2-s2.0-50649124272&doi=10.1038%2fnature07243&partnerID=40&md5=3272b07e00915118b02cb6dbaf2172ce

DOI

10.1038/nature07243

Group (Lab)

J.C. Seamus Davis Group

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