期刊
JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM
卷 22, 期 2, 页码 103-107出版社
SPRINGER
DOI: 10.1007/s10948-008-0393-1
关键词
Electron-phonon interaction; Sound speed anisotropy; Pairing symmetry; Bipolarons; Cuprates
It has gone almost unquestioned that superexchange in the t-J (or Hubbard) model, and not phonons, is responsible for the unconventional (d-wave) pairing symmetry of cuprate superconductors. However, a number of advanced numerical studies have not found superconductivity in the Hubbard (or t-J) model. On the other hand, compelling experimental evidence for a strong electron-phonon interaction (EPI) has currently arrived. Here I briefly review some phonon-mediated unconventional pairing mechanisms. In particular the anisotropy of sound velocity makes the phonon-mediated attraction of electrons non-local in space providing unconventional Cooper pairs with a non-zero orbital momentum already in the framework of the conventional BCS theory with weak EPI. In the opposite limit of strong EPI rotational symmetry breaking appears as a result of a reduced Coulomb repulsion between unconventional bipolarons. Using the variational Monte Carlo method we have found that a relatively weak finite-range EPI induces a d-wave BCS state also in doped Mott-Hubbard insulators or strongly-correlated metals. These results tell us that poorly screened EPI with conventional phonons is responsible for the unconventional pairing in cuprate superconductors.
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