Instability of Nagaoka State and Quantum Phase Transition via Kinetic Frustration Control
arXiv:2508.08410 · doi:10.1103/z4gs-c6h6
Abstract
We investigate the Nagaoka-Thouless (NT) ferromagnetic instability in the strongly interacting - Hubbard model by continuously breaking particle-hole symmetry on a tunable square-triangular lattice geometry. We use an analytic approach to show that the fully spin-polarized state becomes unstable to a metastable spin-polaron when the kinetic frustration exceeds a critical, dimension-dependent value. Large-scale density matrix renormalization group simulations reveal a quantum phase transition from the NT ferromagnet to a spiral spin-density wave, which evolves continuously into the Haerter-Shastry antiferromagnet in the large-frustration limit. Remarkably, this transition remains robust at low but finite hole density, making it accessible in cold-atom and moiré Hubbard platforms under strong interactions. A variational analysis further captures the instability mechanism at finite density via frustration-induced magnon band deformation.
arXiv comment13 pages, 8 figures
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