Rung-singlet phase of the S=1/2 two-leg spin-ladder with four-spin cyclic exchange

TL;DR

This paper uses continuous unitary transformations to analyze the phase transition in a two-leg spin ladder with four-spin exchange, identifying the transition line and crossover behavior.

Contribution

It introduces a novel extrapolation technique to accurately determine the phase transition and crossover in a complex quantum spin system.

Findings

Calculated the one-triplet gap with high-order series expansion.

Determined the transition line between rung-singlet and dimerized phases.

Analyzed the crossover from strong to weak coupling regimes.

Abstract

Using continuous unitary transformations (CUT) we calculate the one-triplet gap for the antiferromagnetic S=1/2 two-leg spin ladder with additional four-spin exchange interactions in a high order series expansion about the limit of isolated rungs. By applying a novel extrapolation technique we calculate the transition line between the rung-singlet phase and a spontaneously dimerized phase with dimers on the legs. Using this efficient extrapolation technique we are able to analyze the crossover from strong rung coupling to weakly coupled chains.