2025/04/16 by Demetrio Vilardi, Vilardi, Demetrio, Pietro M. Bonetti +3 · 2 citations
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Organic and Molecular Conductors Research #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #Strongly Correlated Electrons (cond-mat.str-el)
paper · pdf · doi:10.48550/arxiv.2504.12191
openalex publication_date 2025/04/16 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We analyze the density dependence of the spin stiffnesses and the stability of magnetic order with respect to quantum fluctuations in the two-dimensional Hubbard model close to half-filling. The stiffnesses are computed from the spin susceptibility obtained from a random phase approximation in a magnetically ordered state. For a sizable next-to-nearest neighbor hopping amplitude and a moderate Hubbard interaction, the mean-field ground state is a Néel antiferromagnet in the electron doped regime at and above half-filling, and a planar circular spiral state in the hole doped regime below half-filling. Upon electron doping, the Néel stiffness decreases smoothly and not very steeply. By contrast, the in-plane and out-of-plane stiffnesses in the spiral state drop abruptly at half-filling. The out-of-plane stiffness even drops to zero, and then increases again very slowly upon increasing hole doping. At finite temperatures, the Néel-to-spiral transition is shifted into the hole doped regime, the stiffnesses are continuous functions of the density, and they vanish at the transition. For small hole doping, the spin stiffnesses describe the quantum fluctuations only in a small momentum range, which shrinks to zero upon approaching half-filling. Using the above results, we show that the quantum ground state of the lightly electron doped Hubbard model remains Néel ordered, while quantum fluctuations probably destroy the spiral long-range order in the hole doped regime, giving rise to a quantum disordered state with a spin gap.