Bogoliubov angle and visualization of particle–hole mixture in superconductors
Journal of Physics and Chemistry of Solids Elsevier 69:12 (2008) 3000-3005
Cuprate high-Tc superconductors
Materials Today Elsevier 11:9 (2008) 14-21
Bogoliubov angle and visualization of particle-hole mixture in superconductors
Physical Review B American Physical Society (APS) 78:5 (2008) 054510
How Cooper pairs vanish approaching the Mott insulator in Bi2Sr2CaCu2O8+delta.
Nature 454:7208 (2008) 1072-1078
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.Evolution of the electronic excitation spectrum with strongly diminishing hole density in superconducting Bi2Sr2CaCu2O8+δ
Nature Physics Springer Nature 4:4 (2008) 319-326