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arXiv · 1404.2230

Dispersion-driven ferromagnetism in a flat-band Hubbard system

Oleg Derzhko·Johannes Richter
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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 $U_c$.

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Oleg Derzhko, Johannes Richter. 2014-04-08. Dispersion-driven ferromagnetism in a flat-band Hubbard system. https://doi.org/10.1103/physrevb.90.045152

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