Charge-density waves versus superconductivity in the Holstein model with next-nearest-neighbor hopping.

Abstract

We present quantum Monte Carlo results for the two-dimensional Holstein model with next-nearest-neighbor hopping. The Peierls charge-density-wave (CDW) instability near half filling is significantly suppressed by the addition of the next-nearest-neighbor hopping, and the superconducting pairing in the s-wave channel is enhanced away from half filling. The quantum Monte Carlo results are compared with random-phase-approximation and Migdal-Eliashberg calculations. We estimate the critical temperature for the Peierls CDW transition using a finite-size Ising-like scaling relationship, and for the superconducting transition in an s-wave channel using a Kosterlitz-Thouless scaling analysis. We discuss the possible existence of an incommensurate CDW ordered state away from half filling.