Comparing quantum fluctuations in the spin-$\frac{1}{2}$ and spin-$1$ XXZ Heisenberg models on square and honeycomb lattices

TL;DR

This study uses advanced numerical methods to compare quantum fluctuations in spin-$rac{1}{2}$ and spin-$1$ XXZ Heisenberg models on square and honeycomb lattices, revealing subtle effects of lattice geometry and anisotropy.

Contribution

It introduces Spiral Boundary Conditions (SBC) for efficient 2D to 1D mapping, enabling detailed analysis of quantum fluctuations and magnetization in complex lattice systems.

Findings

Honeycomb lattice shows only marginal reduction in staggered magnetization despite fewer neighbors.

Staggered magnetization dependence on anisotropy matches series expansion predictions away from $\

The spin gap exhibits singular behavior near the isotropic Heisenberg point as predicted by spin-wave theory.

Abstract

We present a detailed investigation of the XXZ Heisenberg model for spin-$1/2$ and spin-$1$ systems on square and honeycomb lattices. Utilizing the density-matrix renormalization group (DMRG) method, complemented by Spiral Boundary Conditions (SBC) for mapping two-dimensional (2D) clusters onto one-dimensional (1D) chains, we meticulously explore the evolution of staggered magnetization and spin gaps across a broad spectrum of easy-axis anisotropies. Our study reveals that, despite the lower site coordination number of honeycomb lattice, which intuitively suggests increased quantum fluctuations in its N\'eel phase compared to the square lattice, the staggered magnetization in the honeycomb structure exhibits only a marginal reduction. Furthermore, our analysis demonstrates that the dependence of staggered magnetization on the XXZ anisotropy $\Delta$, except in close proximity to $\Delta=1$, aligns with series expansion predictions up to the 12th order. Notably, for the $S=1/2$ honeycomb lattice, deviations from the 10th order series expansion predictions near the isotropic Heisenberg limit emphasize the critical influence of quantum fluctuations on the spin excitation in its N\'eel state. Additionally, our findings are numerically consistent with the singular behavior of the spin gap near the isotropic Heisenberg limit as forecasted by spin-wave theory. The successful implementation of SBC marks a methodological advancement, streamlining the computational complexity involved in analyzing 2D models and paving the way for more precise determinations of physical properties in complex lattice systems.