We study the interplay between repulsive interaction and an almost staggered on-site potential in one-dimension. Specifically, we address the Harper model for spinless fermions with nearest-neighbor repulsion, close to half-filling. Using density matrix renormalization group (DMRG), we find that, in contrast to standard behavior, the system becomes more compressible as the repulsive interaction is increased. By generating a low-energy effective model, we unveil the effect of interactions using mean-field analysis: the density of a narrow band around half-filling is anti-correlated with the on-site potential, whereas the density of lower occupied bands follows the potential and strengthens it. As a result, the states around half-filling are squeezed by the background density, their band becomes flatter, and the compressibility increases.
@article{arxiv.1311.4711,
title = {Enhanced compressibility due to repulsive interaction in the Harper model},
author = {Yaacov E. Kraus and Oded Zilberberg and Richard Berkovits},
journal= {arXiv preprint arXiv:1311.4711},
year = {2016}
}