Spin-spiral instability of the Nagaoka ferromagnet in the crossover between square and triangular lattices

• URL: http://arxiv.org/abs/2510.05226v1
• Date: Mon, 06 Oct 2025 18:00:49 GMT
• Title: Spin-spiral instability of the Nagaoka ferromagnet in the crossover between square and triangular lattices
• Authors: Darren Pereira, Erich J. Mueller,
• Abstract summary: We study the hard-core Fermi-Hubbard model in the crossover between square and triangular lattices near half-filling.<n>On the triangular lattice, geometric frustration leads to a spin-singlet ground state, which can be associated with a 120-degree spiral order.<n>We model this instability, finding the exact critical point.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: We study the hard-core Fermi-Hubbard model in the crossover between square and triangular lattices near half-filling. As was recognized by Nagaoka in the 1960s, on the square lattice the presence of a single hole leads to ferromagnetic spin ordering. On the triangular lattice, geometric frustration instead leads to a spin-singlet ground state, which can be associated with a 120-degree spiral order. On lattices which interpolate between square and triangular, there is a phase transition at which the ferromagnetic order becomes unstable to a spin spiral. We model this instability, finding the exact critical point.

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