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arXiv · 2508.08410

Instability of Nagaoka State and Quantum Phase Transition via Kinetic Frustration Control

Prakash Sharma·Yang Peng·Donna N. Sheng·Hitesh J. Changlani·Yao Wang
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Abstract

We investigate the Nagaoka-Thouless (NT) ferromagnetic instability in the strongly interacting $t$-$t'$ 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 $t'/t$ 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 moir\'e Hubbard platforms under strong interactions. A variational analysis further captures the instability mechanism at finite density via frustration-induced magnon band deformation.

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Prakash Sharma, Yang Peng, Donna N. Sheng, Hitesh J. Changlani, Yao Wang. 2025-08-11. Instability of Nagaoka State and Quantum Phase Transition via Kinetic Frustration Control. https://doi.org/10.1103/z4gs-c6h6

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