Magnetic phase diagram of a spin S=1/2 antiferromagnetic two-leg ladder in the presence of modulated along legs Dzyaloshinskii-Moriya interaction

TL;DR

This paper investigates the magnetic phase diagram of a spin-1/2 two-leg ladder with modulated Dzyaloshinskii-Moriya interaction, revealing multiple quantum phase transitions, magnetization plateaus, and the effects of DM interactions on excitation gaps.

Contribution

It introduces a mapping of the ladder model to an effective XXZ chain and analyzes the impact of modulated DM interactions on quantum phases and magnetization plateaus.

Findings

Identified four quantum phase transitions with critical magnetic fields.

Discovered magnetization plateaus at M=0 and M=1, and a gap at M=0.5 due to DM interaction.

Showed the width of the M=0.5 plateau scales with DM parameters as (D0 D1 / J^2)^α.

Abstract

We study the ground-state magnetic phase diagram of a spin S=1/2 antiferromagnetic two-leg ladder in the presence of period two lattice units modulated, Dzyaloshinskii-Moriya (DM) interaction along the legs. We consider the case of collinear DM vectors and strong rung exchange and magnetic field. In this limit we map the initial ladder model onto the effective spin $\sigma=1/2$ XXZ chain and study the latter using the continuum-limit bosonization approach. We identified four quantum phase transitions and corresponding critical magnetic fields, which mark transitions from the spin gapped regimes into the gapless quantum spin-liquid regimes. In the gapped phases the magnetization curve of the system shows plateaus at magnetisation M=0 and to its saturation value per rung M=1. We have shown that the very presence of alternating DM interaction leads to opening of a gap in the excitation spectrum at magnetization M=0.5. The width of the magnetization plateau at M=0.5, is determined by the associated with the dynamical generation of a gap in the spectrum is calculated and is shown that its length scales as $(D_{0}D_{1}/J^{2})^{\alpha}$ where $D_{0},D_{1}$ are uniform and staggered components of the DM term, $J$ is the intraleg exchange and $\alpha \leq 3/4$ and weakly depends on the DM couplings.