Coupled Cluster Treatment of the Alternating Bond Diamond Chain

TL;DR

This paper uses the coupled cluster method and exact diagonalization to analyze the ground and excited states of the alternating bond diamond chain, revealing phase diagrams and confirming the accuracy of CCM in describing various quantum states.

Contribution

The study demonstrates that the coupled cluster method accurately captures the ground states, phase boundaries, and spin gaps of the alternating bond diamond chain, validated by numerical diagonalization.

Findings

Identification of two exact spin cluster solid ground states: TD and dimer states.

CCM accurately determines the spin gap in the TD state.

Critical line between TD and ferrimagnetic states matches ED results.

Abstract

By the analytical coupled cluster method (CCM), we study both the ground state and lowest-lying excited-state properties of the alternating bond diamond chain. The numerical exact diagonalization (ED) method is also applied to the chain to verify the accuracy of CCM results. The ED results show that the ground-state phase diagram contains two exact spin cluster solid ground states, namely, the tetramer-dimer (TD) state and dimer state, and the ferrimagnetic long-range-ordered state. We prove that the two exact spin cluster solid ground states can both be formed by CCM. Moreover, the exact spin gap in the TD state can be obtained by CCM. In the ferrimagnetic region, we find that the CCM results for some physical quantities, such as the ground-state energy, the sublattice magnetizations, and the antiferromagnetic gap, are comparable to the results obtained by numerical methods. The critical line dividing the TD state from the ferrimagnetic state is also given by CCM and is in perfect agreement with that determined by the ED method.