Negative electron compressibility in the Hubbard model

Abstract

Using the strong coupling diagram technique, we study the one-band repulsive Hubbard model on a two-dimensional square lattice in a wide range of chemical potentials μ. Infinite sequences of diagrams describing interactions of electrons with spin and charge fluctuations are taken into account. At low temperatures, regions of the negative electron compressibility are found for μ ≈ 0 and μ ≈ U, where U is the Hubbard repulsion. They are manifestations of non-rigid electron bands, which change drastically in the mentioned regions of chemical potentials due to the level crossing in the Hubbard atom.