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.

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

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