Two topological phases in exchange alternating spin-1 nanographene chains

TL;DR

This paper explores topological phases in spin-1 nanographene chains, identifying conditions for Haldane and dimerized phases, and proposes experimental detection methods.

Contribution

It demonstrates the existence of two topological phases in spin-1 nanographene chains and identifies realistic candidates for their experimental realization.

Findings

Two topological phases identified: Haldane and dimerized.

Biquadratic exchange influences phase transition boundaries.

Proposed experimental detection via inelastic electron tunneling spectroscopy.

Abstract

Magnetic nanographenes are emerging as versatile building blocks for artificial spin lattices, enabling the exploration of flagship one-dimensional quantum-magnetism models with unprecedented control. The spin-1 Heisenberg model, including bilinear and biquadratic exchange, was first realized using [3]-triangulenes, revealing the Haldane phase. More recently, Clar's goblets enabled the spin-1/2 Heisenberg model with exchange alternation, uncovering additional topological phases. Here we show that spin-1 nanographenes can be used to explore bond-alternating chains both in the Haldane phase and beyond it, in a dimerized phase with emergent edge spin-1. We use density matrix renormalization group (DMRG) to analyze how biquadratic exchange, which is known to be large in spin-1 nanographenes, determines the phase transition boundary. Combining multiconfigurational and first-principles calculations, we identify two realistic candidates to realize these two different phases: the recently synthesized extended Clar's goblet and a passivated [4]-triangulene. We demonstrate how to distinguish these phases experimentally using inelastic electron tunneling spectroscopy, paving the way for their observation.