Complete phase diagram for the integrable chain with alternating spins in the sectors with competing interactions

TL;DR

This paper maps the phase diagram of an integrable alternating spin chain with spins 1/2 and 1, revealing a new region with infinite Fermi zones and identifying an additional conformal invariance line.

Contribution

It provides the complete phase diagram for the model, including a novel region with infinite Fermi zones and a new conformal invariance line, using thermodynamic Bethe ansatz analysis.

Findings

Identification of a new phase with infinite Fermi zones.

Calculation of sound velocities from dressed energies.

Discovery of an additional line of conformal invariance.

Abstract

We investigate the anisotropic integrable spin chain consisting of spins $s={1/2}$ and $s=1$ by means of thermodynamic Bethe ansatz for the anisotropy $\gamma>\pi/3$, where the analysis of the Takahashi conditions leads to a more complicated string picture. We give the phase diagram with respect to the two real coupling constants $\bar{c}$ and $\tilde{c}$, which contains a new region where the ground state is formed by strings with infinite Fermi zones. In this region the velocities of sound for the two physical excitations have been calculated from the dressed energies. This leads to an additional line of conformal invariance not known before.