On determining the energy dispersion of spin excitations with scanning tunneling spectroscopy

J. C. G. Henriques; Chenxiao Zhao; G. Catarina; Pascal Ruffieux; Roman Fasel; J. Fernández-Rossier

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arXiv · 2502.13770

On determining the energy dispersion of spin excitations with scanning tunneling spectroscopy

J. C. G. Henriques·Chenxiao Zhao·G. Catarina·Pascal Ruffieux·Roman Fasel·J. Fernández-Rossier

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Abstract

Conventional methods to measure the dispersion relations of collective spin excitations involve probing bulk samples with particles such as neutrons, photons or electrons, which carry a well-defined momentum. Open-ended finite-size spin chains, on the contrary, do not have a well-defined momentum due to the lack of translation symmetry, and their spin excitations are measured with an eminently local probe, using inelastic electron tunneling spectroscopy (IETS) with a scanning tunneling microscope (STM). Here we discuss under what conditions STM-IETS spectra can be Fourier-transformed to yield dispersion relations in these systems. We relate the success of this approach to the degree to which spin excitations form standing waves. We show that STM-IETS can reveal the energy dispersion of magnons in ferromagnets and triplons in valence bond crystals, but not that of spinons, the spin excitations in Heisenberg spin-1/2 chains. We compare our theoretical predictions with state-of-the-art measurements on nanographene chains that realize the relevant spin Hamiltonians.

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J. C. G. Henriques, Chenxiao Zhao, G. Catarina, Pascal Ruffieux, Roman Fasel, J. Fernández-Rossier. 2025-02-19. On determining the energy dispersion of spin excitations with scanning tunneling spectroscopy. https://arxiv.org/abs/2502.13770

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