Effects of a space modulation on the behavior of a 1D alternating Heisenberg spin-1/2 model

TL;DR

This study investigates how space modulation and magnetic fields influence the quantum phases and magnetic properties of a 1D antiferromagnetic-ferromagnetic Heisenberg spin-1/2 chain, revealing new gapped phases and magnetization plateaus.

Contribution

It introduces the effects of space modulation on the model's phase diagram, showing the emergence of a magnetization plateau and new quantum phases not previously characterized.

Findings

Space modulation induces a new energy gap in the system.

A magnetization plateau at half saturation appears due to the gap.

Multiple quantum phase transitions occur at critical magnetic fields.

Abstract

The effects of a magnetic field ($h$) and a space modulation ($\delta$) on the magnetic properties of a one dimensional antiferromagnetic-ferromagnetic Heisenberg spin-1/2 model have been studied by means of numerical exact diagonalization of finite size systems, nonlinear sigma model and bosonization approach. The space modulation is considered on the antiferromagnetic couplings. At $\delta=0$, the model is mapped to a gapless L\"{u}ttinger liquid phase by increasing the magnetic field. However, the space modulation induces a new gap in the spectrum of the system and the system experiences different quantum phases which are separated by four critical fields. By opening the new gap a magnetization plateau appears at ${1/2}M_{sat}$. The effects of the space modulation are reflected in the emergence of a plateau in other physical functions such as the F-dimer and the bond dimer order parameters, and the pair-wise entanglement.