Fermi Condensation Near van Hove Singularities Within the Hubbard Model on the Triangular Lattice

TL;DR

This paper investigates how strong correlations near van Hove singularities in the Hubbard model on a triangular lattice lead to flat band formation, revealing new physics that can be experimentally observed in ultracold atom systems.

Contribution

It provides a detailed analytical and numerical analysis of Fermi condensation near van Hove singularities within the Hubbard model on a triangular lattice, highlighting correlation-driven band flattening.

Findings

Band flattening driven by correlations is significant at high temperatures.

The effect is observable in ultracold fermion experiments.

Both weak and strong coupling approaches confirm the phenomenon.

Abstract

The proximity of the Fermi surface to van Hove singularities drastically enhances interaction effects and leads to essentially new physics. In this work we address the formation of flat bands ("Fermi condensation") within the Hubbard model on the triangular lattice and provide a detailed analysis from an analytical and numerical perspective. To describe the effect we consider both weak-coupling and strong-coupling approaches, namely the renormalization group and dual fermion methods. It is shown that the band flattening is driven by correlations and is well pronounced even at sufficiently high temperatures, of the order of 0.1-0.2 of the hopping parameter. The effect can therefore be probed in experiments with ultracold fermions in optical lattices.