# Magnon excitations in $Cs_2CuAl_4O_8$ - a bond alternating S=1/2 spin chain with next nearest neighbor coupling

## TL;DR

This paper investigates magnon excitations in the frustrated one-dimensional $Cs_2CuAl_4O_8$ spin chain, revealing multiple magnon modes that are stable only without bond alternations, combining DFT and Quantum Monte Carlo insights.

## Contribution

It provides a theoretical analysis of magnon excitations in a complex spin chain with bond alternations and next nearest neighbor interactions, highlighting stability conditions.

## Key findings

- Multiple magnon modes are predicted in the ground state.
- Magnon modes are stable only without bond alternations.
- The study combines DFT and Quantum Monte Carlo methods.

## Abstract

A recent density functional theory (DFT) based analysis, complemented with Quantum Monte Carlo calculations revealed a highly spin-frustrating nature of the one-dimensional spin-$\frac{1}{2}$ compound $Cs_2CuAl_4O_8$ that comprises of unique bond alternations and relatively strong next nearest neighbor interactions. This article gives a brief account on possible magnon excitations that can appear in the ground state of such systems. We find that the spin waves obtained on top of coplanar helical reference states show multiple magnon modes (both acoustic and optical). However, those magnon modes turn out to be stable only in the absence of bond alternations.