Dispersion-driven ferromagnetism in a flat-band Hubbard system

Abstract

We investigate a mechanism to establish ground-state ferromagnetism in flat-band Hubbard systems based on a kind of {\it order-from-disorder} effect driven by dispersion. As a paradigm we consider a frustrated diamond chain, where for ideal diamond geometry the lowest one-electron band is flat, but the ground state remains paramagnetic for arbitrary on-site repulsion $U$. We focus on half filling of the flat band. By using numerical and analytical arguments we present the ground-state phase diagram for a distorted diamond chain, i.e., the former flat band becomes dispersive. Driven by the interplay of dispersion and interaction the ground state is ferromagnetic if the interaction exceeds a critical value $U_c$.

arXiv comment7 pages, 3 figures

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• Strongly correlated flat-band systems: The route from Heisenberg spins to Hubbard electrons
• Flat-band ferromagnetism in a topological Hubbard model
• Fermi-liquid Landau parameters for a nondegenerate band: Spin and charge instabilities in the extended Hubbard model
• Low temperature pseudo-phase transition in an extended Hubbard diamond chain
• Hubbard models with nearly flat bands: Ground-state ferromagnetism driven by kinetic energy
• Certain exact many-body results for Hubbard model ground states testable in small quantum dot arrays
• Pentagon chain in external fields
• Flat band ferromagnetism without connectivity conditions in the flat band
• Phase diagram of a coupled trimer system at half filling using the Hubbard model