Article,
Relating atomic-scale electronic phenomena to wave-like quasiparticle states in superconducting Bi2Sr2CaCu2O8+delta
Nature, 422 (6932): 592--596 (April 2003)
Abstract
The electronic structure of simple crystalline solids can be completely
described in terms either of local quantum states in real space (r-space),
or of wave-like states defined in momentum-space (k-space). However,
in the copper oxide superconductors, neither of these descriptions
alone may be sufficient. Indeed, comparisons between r-space1, 2,
3, 4, 5 and k-space6, 7, 8, 9, 10, 11, 12, 13 studies of Bi2Sr2CaCu2O8+
(Bi-2212) reveal numerous unexplained phenomena and apparent contradictions.
Here, to explore these issues, we report Fourier transform studies
of atomic-scale spatial modulations in the Bi-2212 density of states.
When analysed as arising from quasiparticle interference14, 15, 16,
the modulations yield elements of the Fermi-surface and energy gap
in agreement with photoemission experiments12, 13. The consistency
of numerous sets of dispersing modulations with the quasiparticle
interference model shows that no additional order parameter is required.
We also explore the momentum-space structure of the unoccupied states
that are inaccessible to photoemission, and find strong similarities
to the structure of the occupied states. The copper oxide quasiparticles
therefore apparently exhibit particle–hole mixing similar to that
of conventional superconductors. Near the energy gap maximum, the
modulations become intense, commensurate with the crystal, and bounded
by nanometre-scale domains4. Scattering of the antinodal quasiparticles
is therefore strongly influenced by nanometre-scale disorder.
