Magnetism of one-dimensional strongly repulsive spin-1 bosons with antiferromagnetic spin exchange interaction

TL;DR

This paper studies the magnetic phases and quantum phase transitions of one-dimensional strongly repulsive spin-1 bosons with antiferromagnetic interactions, revealing three distinct phases and the effects of temperature and magnetic field on their thermodynamics.

Contribution

It provides an exact analysis of the phase diagram and thermodynamics of the model using the thermodynamic Bethe ansatz, highlighting the interplay of spin fluctuations and external magnetic fields.

Findings

Identification of three quantum phases: singlet, ferromagnetic, and mixed.

Finite temperature effects couple spin bound states to unpaired bosons.

Strong magnetic fields suppress spin fluctuations, enabling a two-component Luttinger liquid.

Abstract

We investigate magnetism and quantum phase transitions in a one-dimensional system of integrable spin-1 bosons with strongly repulsive density-density interaction and antiferromagnetic spin exchange interaction via the thermodynamic Bethe ansatz method. At zero temperature, the system exhibits three quantum phases: (i) a singlet phase of boson pairs when the external magnetic field $H$ is less than the lower critical field $H_{c1}$; (ii) a ferromagnetic phase of atoms in the hyperfine state $|F=1, m_{F}=1>$ when the external magnetic field exceeds the upper critical field $H_{c2}$; and (iii) a mixed phase of singlet pairs and unpaired atoms in the intermediate region $H_{c1}<H<H_{c2}$. At finite temperatures, the spin fluctuations affect the thermodynamics of the model through coupling the spin bound states to the dressed energy for the unpaired $m_{F}=1$ bosons. However, such spin dynamics is suppressed by a sufficiently strong external field at low temperatures. Thus the singlet pairs and unpaired bosons may form a two-component Luttinger liquid in the strong coupling regime.