Phase diagram of S=1/2 two-leg XXZ spin ladder systems

TL;DR

This paper maps the phase diagram of the S=1/2 two-leg XXZ spin ladder, identifying phase boundaries and the existence of two distinct XY phases using advanced numerical methods.

Contribution

It introduces a combined level spectroscopy and twisted boundary condition approach to accurately determine phase transitions in the model.

Findings

The XY-Haldane and XY-rung singlet phase boundaries involve Berezinskii-Kosterlitz-Thouless transitions.

The phase boundary between XY and Haldane phases is on the $ ext{Δ}=0$ line.

Two different XY phases are distinguished by their $XX$ correlation functions.

Abstract

We investigate the ground state phase diagram of the S=1/2 two-leg $XXZ$ spin ladder system with an isotropic interchain coupling. In this model, there is the Berezinskii-Kosterlitz-Thouless transition which occurs at the XY-Haldane and the XY-rung singlet phase boundaries. It was difficult to determine the transition line using traditional methods. We overcome this difficulty using the level spectroscopy method combined with the twisted boundary condition method, and we check the consistency. We find out that the phase boundary between XY phase and Haldane phase lies on the $\Delta=0$ line. And we show that there exist two different XY phases, which we can distinguish investigating a $XX$ correlation function.