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Observation of fractional edge excitations in nanographene spin chains

Shantanu Mishra1,2*, Gonçalo Catarina3,4, Fupeng Wu5, Ricardo Ortiz4, David Jacob6,7, Kristjan Eimre1*, Ji Ma5, Carlo A. Pignedoli1, Xinliang Feng5,8, Pascal Ruffieux1*, Joaquín Fernández-Rossier3, Roman Fasel1,9

1 Empa - Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland

2 Present address: IBM Research – Zurich, Rüschlikon, Switzerland

3 International Iberian Nanotechnology Laboratory, Braga, Portugal

4 University of Alicante, Sant Vicent del Raspeig, Spain

5 Technical University of Dresden, Dresden, Germany

6 University of the Basque Country, San Sebastián, Spain

7 IKERBASQUE, Basque Foundation for Science, Bilbao, Spain

8 Max Planck Institute of Microstructure Physics, Halle, Germany

9 University of Bern, Bern, Switzerland

* Corresponding authors emails: SHM@zurich.ibm.com, kristjan.eimre@empa.ch, pascal.ruffieux@empa.ch
DOI10.24435/materialscloud:e8-aq [version v1]

Publication date: Oct 11, 2021

How to cite this record

Shantanu Mishra, Gonçalo Catarina, Fupeng Wu, Ricardo Ortiz, David Jacob, Kristjan Eimre, Ji Ma, Carlo A. Pignedoli, Xinliang Feng, Pascal Ruffieux, Joaquín Fernández-Rossier, Roman Fasel, Observation of fractional edge excitations in nanographene spin chains, Materials Cloud Archive 2021.161 (2021), doi: 10.24435/materialscloud:e8-aq.


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, solitons in one-dimensional conducting polymers and Majorana states in topological superconductors. 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 bulk and, remarkably, S = 1/2 edge states at the chain termini, leading to a four-fold degenerate ground state that reflects the underlying symmetry-protected topological order. This record contains data to support the result in a recent publication of ours where we use on-surface synthesis to fabricate one-dimensional spin chains that contain the S = 1 polycyclic aromatic hydrocarbon triangulene as the building block. Using scanning tunneling 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 computation.

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File name Size Description
73.9 KiB ReadME file in yaml format detailing the content of the record
59.4 MiB Compressed tar file containing the experimental data and the gw calculations of the record
Open this AiiDA archive on renkulab.io (https://renkulab.io/)
13.2 GiB Archive of AiiDA nodes of the bandstructure calculations


Files and data are licensed under the terms of the following license: Creative Commons Attribution 4.0 International.
Metadata, except for email addresses, are licensed under the Creative Commons Attribution Share-Alike 4.0 International license.

External references

Journal reference (Manuscript where the results are discussed)
S. Mishra, G. Catarina, F. Wu, R. Ortiz, D. Jacob, K. Eimre, J. Ma, C. A. Pignedoli, X. Feng, P. Ruffieux, J. Fernández-Rossier, R. Fasel, Nature (2021) doi:10.1038/s41586-021-03842-3
Preprint (open access version of the manuscript)


spin chains nanographene fractionalization Graphene flagship MARVEL/DD3 ERC CSCS H2020 SNSF

Version history:

2021.161 (version v1) [This version] Oct 11, 2021 DOI10.24435/materialscloud:e8-aq