# Spin excitations and thermodynamics of the antiferromagnetic Heisenberg model on the layered honeycomb lattice

## TL;DR

This paper develops a Green-function theoretical approach to study spin excitations and thermodynamics in the antiferromagnetic Heisenberg model on a layered honeycomb lattice, providing insights into magnetic properties and phase transitions.

## Contribution

It introduces a spin-rotation-invariant Green-function method with a generalized mean-field approximation for arbitrary temperatures, enabling calculation of thermodynamic quantities and spin spectra.

## Key findings

- Good agreement with numerical cluster computations
- Accurate prediction of N'eel temperature for various interlayer couplings
- Reproduction of experimental data on -Cu2V2O2

## Abstract

We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic Heisenberg model on a stacked honeycomb lattice. Employing a generalized mean-field approximation for arbitrary temperatures, the thermodynamic quantities (two-spin correlation functions, internal energy, magnetic susceptibility, staggered magnetization, N'eel temperature, correlation length) and the spin-excitation spectrum are calculated by solving a coupled system of self-consistency equations for the correlation functions. The temperature dependence of the magnetic (uniform static) susceptibility is ascribed to antiferromagnetic short-range order. The N\'{e}el temperature is calculated for arbitrary interlayer couplings. Our results are in a good agreement with numerical computations for finite clusters and with available experimental data on the \beta-Cu2V2O2 compound.