Multi-magnon bound states in the frustrated ferromagnetic 1D chain

TL;DR

This paper investigates a 1D frustrated ferromagnetic chain, revealing that bound multi-magnon states dominate excitations and can lead to exotic quantum liquids with nematic and triatic orderings.

Contribution

It provides a detailed analysis of multi-magnon bound states and their role in forming novel quantum phases in a frustrated 1D ferromagnetic system.

Findings

Bound multi-magnon states are always lowest excitations except in small parameter ranges.

Bose condensation of these bound states leads to Tomonaga-Luttinger liquids with multi-polar correlations.

Identification of nematic and triatic ordered liquids corresponding to n=2 and n=3 bound magnons.

Abstract

We study a one-dimensional Heisenberg chain with competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest neighbor interactions in magnetic field. Starting from the fully polarized high-field state, we calculate the dispersions of the lowest-lying $n$-magnon excitations and the saturation field (n=2,3,4). We show that the lowest-lying excitations are always bound multi-magnon states with a total momentum of $\pi$ except for a small parameter range. We argue that bose condensation of the bound $n$ magnons leads to novel Tomonaga-Luttinger liquids with multi-polar correlations; nematic and triatic ordered liquids correspond to n=2 and n=3.