Staggered dimer order in S=1/2 quantum spin ladder system with four spin exchange

TL;DR

This paper investigates the phase transition and order in a S=1/2 quantum spin ladder with four-spin exchange, using numerical methods to clarify the nature of the phase transition and the emergence of edge states.

Contribution

The study introduces a new approach to identify phases post-transition by analyzing edge states and excitation energies, clarifying the nature of the phase transition.

Findings

Edge states appear in open boundary conditions.

Analysis suggests a staggered dimer order in the system.

Clarifies the nature of the phase transition and order parameter.

Abstract

We study the S=1/2 quantum spin ladder system with the four-spin exchange, using density matrix renormalization group method and an exact diagonalization method. Recently, the phase transition in this system and its universality class are studied. But there remain controversies whether the phase transition is second order type or the other type and the nature of order parameter. There are arguments that the massless phase appears. But this does not agree with our previous result. Analyzing DMRG data, we try a new approach in order to determine a phase which appears after the phase transition. We find that the edge state appears in the open boundary condition, investigating excitation energies of states with higher magnetizations.