Author
Listed:
- Shantanu Mishra
(Empa—Swiss Federal Laboratories for Materials Science and Technology
IBM Research—Zurich)
- Gonçalo Catarina
(International Iberian Nanotechnology Laboratory
University of Alicante)
- Fupeng Wu
(Technical University of Dresden)
- Ricardo Ortiz
(University of Alicante)
- David Jacob
(University of the Basque Country
IKERBASQUE, Basque Foundation for Science)
- Kristjan Eimre
(Empa—Swiss Federal Laboratories for Materials Science and Technology)
- Ji Ma
(Technical University of Dresden)
- Carlo A. Pignedoli
(Empa—Swiss Federal Laboratories for Materials Science and Technology)
- Xinliang Feng
(Technical University of Dresden
Max Planck Institute of Microstructure Physics)
- Pascal Ruffieux
(Empa—Swiss Federal Laboratories for Materials Science and Technology)
- Joaquín Fernández-Rossier
(International Iberian Nanotechnology Laboratory)
- Roman Fasel
(Empa—Swiss Federal Laboratories for Materials Science and Technology
University of Bern)
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 effect1,2, solitons in one-dimensional conducting polymers3,4 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 termini7–9, leading to a four-fold degenerate ground state that reflects the underlying symmetry-protected topological order10,11. 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.
Suggested Citation
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, 2021.
"Observation of fractional edge excitations in nanographene spin chains,"
Nature, Nature, vol. 598(7880), pages 287-292, October.
Handle:
RePEc:nat:nature:v:598:y:2021:i:7880:d:10.1038_s41586-021-03842-3
DOI: 10.1038/s41586-021-03842-3
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