The Double-Time Green's Function Approach to the Two-Dimensional Heisenberg Antiferromagnet with Broken Bonds

TL;DR

This paper advances the double-time Green's function method to analyze the effects of broken bonds in the two-dimensional spin-1/2 antiferromagnetic Heisenberg model, revealing temperature-dependent quantum fluctuations and interactions.

Contribution

It introduces an improved decoupling approximation applicable to inhomogeneous spin systems with defects across all temperatures.

Findings

Quantum fluctuation reduced near broken bonds at low temperatures.

Quantum fluctuation enhanced near broken bonds at high temperatures.

Repulsive interaction observed between parallel broken bonds at low temperatures.

Abstract

We improved the decoupling approximation of the double-time Green's function theory, and applied it to study the spin-${1\over 2}$ two-dimensional antiferromagnetic Heisenberg model with broken bonds at finite temperature. Our decoupling approximation is applicable to the spin systems with spatial inhomogeneity, introduced by the local defects, over the whole temperature region. At low temperatures, we observed that the quantum fluctuation is reduced in the neighborhood of broken bond, which is in agreement with previous theoretical expectations. At high temperatures our results showed that the quantum fluctuation close to the broken bond is enhanced. For the two parallel broken bonds cases, we found that there exists a repulsive interaction between the two parallel broken bonds at low temperatures.