Topological Phases of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain with Frustrated Next-Nearest-Neighbour Interaction

TL;DR

This paper explores the topological phases of a spin-1/2 alternating Heisenberg chain with frustrated NNN interactions, revealing multiple distinct spin-gap phases and their phase boundaries through DMRG calculations.

Contribution

It identifies and characterizes a series of topologically distinct spin-gap phases with varying edge spins in the model, expanding understanding of topological phases in quantum spin chains.

Findings

Multiple topologically distinct spin-gap phases identified

Phase boundaries determined using DMRG with edge spin compensation

Exact solutions represent each spin gap phase at phase boundaries

Abstract

The spin-1/2 ferromagnetic-antiferromagnetic alternating Heisenberg chain with ferromagnetic next-nearest-neighbour (NNN) interaction is investigated. The ground state is the Haldane phase for weak NNN interaction, and is the ferromagnetic phase for weak antiferromagnetic interaction. We find a series of topologically distinct spin-gap phases with various magnitudes of edge spins for strong NNN interaction. The phase boundaries between these phases are determined on the basis of the DMRG calculation with additional spins that compensate the edge spins. It is found that each of the exact solutions with short-range antiferromagnetic correlation on the ferromagnetic-nonmagnetic phase boundary is representative of each spin gap phase.