paper

Breakdown of Migdal-Eliashberg theory; a determinant quantum Monte Carlo study

arXiv:1711.01493 · doi:10.1103/PhysRevB.97.140501

Abstract

The superconducting (SC) and charge-density-wave (CDW) susceptibilities of the two dimensional Holstein model are computed using determinant quantum Monte Carlo (DQMC), and compared with results computed using the Migdal-Eliashberg (ME) approach. We access temperatures as low as 25 times less than the Fermi energy, , which are still above the SC transition. We find that the SC susceptibility at low agrees quantitatively with the ME theory up to a dimensionless electron-phonon coupling but deviates dramatically for larger . We find that for large and small phonon frequency CDW ordering is favored and the preferred CDW ordering vector is uncorrelated with any obvious feature of the Fermi surface.

arXiv comment7 pages, 7 figures. v2: discussion improved, added supplemental material

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