Observation of fractional edge excitations in nanographene spin chains

Mishra S, Catarina G, Wu F, Ortiz R, Jacob D, Eimre K, Ma J, Pignedoli CA, Feng X, Ruffieux P, Fernandez-Rossier J, Fasel R (2021)

Publication Type: Journal article

Publication year: 2021

Journal

Nature Nature Research

Book Volume: 598

Pages Range: 287-292

Journal Issue: 7880

DOI: 10.1038/s41586-021-03842-3

Abstract

Fractionalization is a phenomenon in which strong interactions in a quantum system drive the emergence of excitations with quantum numbers that are absent in the building blocks. Outstanding examples are excitations with charge e/3 in the fractional quantum Hall effect^1,2, solitons in one-dimensional conducting polymers^3,4 and Majorana states in topological superconductors⁵. Fractionalization is also predicted to manifest itself in low-dimensional quantum magnets, such as one-dimensional antiferromagnetic S = 1 chains. The fundamental features of this system are gapped excitations in the bulk⁶ and, remarkably, S = 1/2 edge states at the chain termini^7–9, leading to a four-fold degenerate ground state that reflects the underlying symmetry-protected topological order^10,11. Here, we use on-surface synthesis¹² to fabricate one-dimensional spin chains that contain the S = 1 polycyclic aromatic hydrocarbon triangulene as the building block. Using scanning tunnelling microscopy and spectroscopy at 4.5 K, we probe length-dependent magnetic excitations at the atomic scale in both open-ended and cyclic spin chains, and directly observe gapped spin excitations and fractional edge states therein. Exact diagonalization calculations provide conclusive evidence that the spin chains are described by the S = 1 bilinear-biquadratic Hamiltonian in the Haldane symmetry-protected topological phase. Our results open a bottom-up approach to study strongly correlated phases in purely organic materials, with the potential for the realization of measurement-based quantum computation¹³.

Involved external institutions

Technische Universität Dresden

Germany (DE) University of Alicante / Universidad de Alicante / Universitat d'Alacant

Spain (ES) Eidgenössische Materialprüfungs- und Forschungsanstalt (Empa) / Swiss Federal Laboratories for Materials Science & Technology

Switzerland (CH) INL - International Iberian Nanotechnology Laboratory

Portugal (PT) University of Basque Country / Universidad del Pais Vasco (UPV) / Euskal Herriko Unibersitatea (EHU)

Spain (ES)

How to cite

APA:

Mishra, S., Catarina, G., Wu, F., Ortiz, R., Jacob, D., Eimre, K.,... Fasel, R. (2021). Observation of fractional edge excitations in nanographene spin chains. Nature, 598(7880), 287-292. https://doi.org/10.1038/s41586-021-03842-3

MLA:

Mishra, Shantanu, et al. "Observation of fractional edge excitations in nanographene spin chains." Nature 598.7880 (2021): 287-292.

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