Quantum Phase Transition of S=1/2 Trimerized XXZ Spin Chain in Magnetic Field

TL;DR

This paper investigates the quantum phase transition related to magnetization plateaus in a trimerized S=1/2 XXZ spin chain, identifying the transition type and precise phase boundary using numerical methods.

Contribution

It provides a detailed numerical analysis of the Berezinskii-Kosterlitz-Thouless transition in the spin chain, including a method to accurately determine the phase boundary.

Findings

Identification of the plateauful-plateauless transition as a BKT-type quantum phase transition.

Precise determination of the phase boundary using level crossing analysis.

Discussion of the ferromagnetic-ferromagnetic-antiferromagnetic chain case.

Abstract

We study the magnetization plateau at a third of the saturation magnetization of the S=1/2 trimerized XXZ spin chain at T=0. The appearance of the plateau depends on the values of the XXZ anisotropy and the magnitude of the trimerization. This plateauful-plateauless transition is a quantum phase transition of the Berezinskii-Kosterlitz-Thouless type, which is difficult to precisely detect from the numerical data. To determine the phase boundary line of this transition precisely, we use the level crossing of low-lying excitations obtained from the numerical diagonalization. We also discuss the S=1/2 ferromagnetic-ferromagnetic-antiferromagnetic chain.