Exact spin-cluster ground states in a mixed diamond chain

TL;DR

This paper investigates the ground states of a frustrated mixed diamond Heisenberg chain, identifying exact spin cluster states and phase diagrams across different parameters, revealing rich quantum phases.

Contribution

It proves the existence of exact spin cluster ground states in a finite parameter range and maps the phase diagram for S=1.

Findings

Identification of exact spin cluster ground states

Phase diagram with five distinct phases for S=1

Ground states depend on the frustration parameter lambda

Abstract

The mixed diamond chain is a frustrated Heisenberg chain composed of successive diamond-shaped units with two kinds of spins of magnitudes S and S/2 (S: integer). Ratio $lambda$ of two exchange parameters controls the strength of frustration. With varying $lambda$, the Haldane state and several spin cluster states appear as the ground state. A spin cluster state is a tensor product of exact local eigenstates of cluster spins. We prove that a spin cluster state is the ground state in a finite interval of $lambda$. For S=1, we numerically determine the total phase diagram consisting of five phases.