The role of correlated hopping in many-body physics of flat-band systems: Nagaoka ferromagnetism

TL;DR

This paper investigates how correlated hopping processes influence the emergence of ferromagnetic states in flat-band systems, revealing the distinct roles of different hopping types through exact diagonalization.

Contribution

It introduces a detailed analysis of correlated hopping processes in flat-band systems and their impact on Nagaoka ferromagnetism, which was not thoroughly explored before.

Findings

Correlated hopping processes are crucial for flat-band ferromagnetism.

Different hopping types have distinct roles in many-body effects.

Exact diagonalization confirms the importance of these processes in ferromagnetic state formation.

Abstract

In narrow-band systems, correlated contribution to effective hopping becomes important, and one needs to carefully consider three types of hopping processes: between doubly and singly occupied sites, between singly occupied and empty sites, and between doubly occupied and empty or two singly occupied sites. All three hopping parameters cannot vanish simultaneously, and one should specify for which of these processes the band becomes flat. By means of exact diagonalization of finite systems we demonstrate that three hoppings play qualitatively different roles in many-body effects, in particular, in the formation of half-metallic ferromagnetic (Nagaoka) states.