Tunable Topological Phases Enable Novel Quantum Materials with Protected Edge Spins

The pursuit of stable, interacting topological phases in real-world materials remains a significant challenge in condensed matter physics, but new research demonstrates a promising pathway using organic molecules. Khalid N. Anindya and Hong Guo, both from McGill University, alongside their colleagues, reveal that a specifically designed organic chain exhibits two distinct symmetry-protected topological phases. Their work identifies an unusual “odd-Haldane” phase and a more conventional Haldane phase, both arising from the unique electronic properties of the material and tunable through chemical modification. This achievement establishes a chemically programmable molecular platform for exploring interacting topological physics in one dimension and suggests potential applications for nanoscale devices based on organic Haldane spin chains.

Carbon Chain Structure and Magnetic Properties Scientists have investigated the structural and magnetic properties of novel carbon-based chains using advanced computational techniques and simulations.

This research provides a detailed understanding of these materials, paving the way for potential applications in nanotechnology.

The team utilized density functional theory and density matrix renormalization group calculations to model the electronic structure and ground state properties of the chains. Molecular dynamics simulations, crucial for accurately describing the complex bonding within these materials, confirmed the structural integrity of the chains at 300 Kelvin. Thermal motion is localized at the junctions and substituents, while the aromatic backbone remains rigid, generating accurate geometries and fluctuation data for subsequent calculations. The research quantified the thermal expansion behavior of the carbon chains, determining the linear thermal expansion coefficient and confirming its consistency with observed structural stability. Diagnostic tools, such as end-to-end distance and transverse fluctuations, validated the accuracy and reproducibility of the simulations, providing a robust understanding of the structural and thermal properties of these complex materials.

Tunable Topological Phases in Organic Chains Scientists have discovered a chemically programmable molecular platform capable of hosting two distinct symmetry-protected topological phases within a single organic chain. This breakthrough offers a route towards nanoscale quantum devices by realizing both an odd-Haldane phase and a Haldane phase within a tunable, one-dimensional system, offering potential for edge-spin qubits and topological spin-transport components. Experiments reveal that the system, based on carbonyl-triphenyl derivatives, supports two archetypal SPT phases through distinct radicalization patterns. A single radical per monomer yields a spin-1/2 lattice, while two radicals coupled via Hund’s rule form spin-1 superatoms. Density-functional theory calculations place the active electronic manifold deep within the Mott regime, justifying a simplified spin-only Heisenberg description.

The team established SPT order using key diagnostics, confirming a quantized many-body Zak phase, an even-degenerate entanglement spectrum, and termination-dependent ground-state multiplets. Analysis of S+−(q, ω) reveals characteristic triplon/Haldane features, providing a dynamical fingerprint of the topological order. The odd-Haldane phase exhibits a dispersive one-triplon branch, while the Haldane phase displays a finite bulk gap and S=1/2 edge states. The research demonstrates that cutting the chain at different bonds selects the SPT sector in the odd-Haldane phase, yielding either an even-Haldane termination with two spin-1/2 edge modes or a trivial ground state. In contrast, the Haldane phase supports a near-fourfold ground-state manifold independent of chain termination. This comparability, arising from the same molecular backbone and protecting symmetries, allows for direct assessment of the two phases within a single chemical framework, establishing a powerful platform for exploring interacting SPT physics in one dimension.

Tunable Topological Phases in Organic Molecules This research demonstrates the existence of symmetry-protected topological phases within a chemically realistic organic molecule, a significant step towards realizing practical topological quantum materials.

Scientists have identified that a specifically designed one-dimensional chain, based on a nitrogen-doped carbonyl-triphenyl platform, can host two distinct interacting SPT phases: an odd-Haldane phase and a Haldane phase. Detailed analysis using a combination of computational methods, including density-functional theory, exact diagonalization, and density-matrix renormalization group, confirms the topological nature of these phases. Key indicators, such as a quantized Zak phase, an even-degenerate entanglement spectrum, and protected edge spins, were consistently observed across both phases, establishing a strong connection between microscopic exchange interactions and emergent triplon dynamics. Importantly, calculations indicate that the stability of these topological states extends to room temperature, suggesting potential for practical applications in nanoscale devices and quantum simulation. This work establishes a promising new platform for exploring and harnessing the unique properties of interacting SPT phases in one dimension, providing a foundation for future advancements in topological quantum materials and nanoscale devices. 👉 More information 🗞 Tunable Topological Phases in an Organic One-Dimensional Mott Chain: Odd-Haldane (S = 1/2) and Haldane (S = 1) 🧠 ArXiv: https://arxiv.org/abs/2512.16173 Tags: