Frustrated spin chains in strong magnetic field: dilute two-component Bose gas regime

TL;DR

This paper investigates the ground state phases of frustrated spin chains near saturation, modeling them as a dilute two-component magnon Bose gas, and predicts phase transitions including chiral and bound magnon phases.

Contribution

It develops a quantitative theory of effective magnon interactions in frustrated spin chains near saturation for arbitrary spin values.

Findings

Established the magnetic phase diagram near saturation.

Predicted phase transitions including two-component Luttinger liquid and chiral phases.

Numerical results agree with analytical predictions.

Abstract

We study the ground state of frustrated spin-S chains in a strong magnetic field in the immediate vicinity of saturation. In strongly frustrated chains, the magnon dispersion has two degenerate minima at inequivalent momenta $\pm Q$, and just below the saturation field the system can be effectively represented as a dilute one-dimensional lattice gas of two species of bosons that correspond to magnons with momenta around $\pm Q$. We present a theory of effective interactions in such a dilute magnon gas that allows us to make quantitative predictions for arbitrary values of the spin. With the help of this method, we are able to establish the magnetic phase diagram of frustrated chains close to saturation and study phase transitions between several nontrivial states, including a two-component Luttinger liquid, a vector chiral phase, and phases with bound magnons. We study those phase transitions numerically and find a good agreement with our analytical predictions.