Magnetic fluctuations near the Van Hove singularity in the kagome-lattice Hubbard model at finite doping

Abstract

The kagome-lattice Hubbard model attracts widespread interest due to its flat-band and Van Hove singularity features, which can give rise to unconventional magnetism. We employ determinant quantum Monte Carlo simulations to systematically investigate the uniform magnetic susceptibility across a range of on-site interactions and electron fillings on a two-dimensional kagome lattice. Beyond the Van Hove singularity, dominant ferromagnetic fluctuations emerge. Magnetic susceptibility grows markedly with increasing interaction strength and decreasing temperature, indicating that the Van Hove singularity acts as a critical point for the crossover of dominant magnetic fluctuations. Finite-size analysis further suggests the potential stabilization of a finite-temperature ferromagnetic phase. We also examine the sign problem to identify numerically reliable parameter regimes. These results provide valuable insights into controlling magnetic fluctuations in kagome systems and establish a computational framework for exploring flat-band physics in regimes characterized by novel quantum phases and competing orders.

Figures (7)

• Figure 1: (a) The structure of the kagome lattice. In each unit cell (gray triangles), the sublattice is labeled as A (yellow dots), B (red dots), and C (green dots). (b) The Brillouin zone of the kagome lattice. (c) The band structure of the tight-binding kagome model along the high-symmetry direction. (d) Density of states (DOS) (solid lines) and filling $\langle n\rangle$ (dashed lines) as functions of energy.
• Figure 2: The average sign as a function of electron filling $\left\langle n\right\rangle$ for different temperature $T$. Even at the lowest temperatures, ⟨sign⟩ remains above 0.45 in the crossover regime, ensuring numerical reliability. The error is controlled within 4.4$\times$10$^{-4}$.
• Figure 3: The temperature-dependent z-component spin susceptibility $\chi_z$ at $U$=3.0$t$ with different fillings $\left\langle n\right\rangle$.
• Figure 4: The uniform spin magnetic susceptibility vs electron doping concentration at different values of $T$ with $U=3.0t$ and $U=4.0t$.
• Figure 5: Uniform spin susceptibility $\chi_z$ as a function of $T$ with various $L=4,6,8$ at $\left\langle n\right\rangle=1.3, 1.4, 1.5$. Calculations are based on $U=3.0t$ system.