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Identification and optimization of accurate spin models for Fermi-Hubbard ladders using matrix product states

Andoni Agirre1,2,*, Thomas Frederiksen1,3, Géza Giedke1,3, and Tobias Graß1,3

  • *Contact author: andoni.agirre@dipc.org
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Phys. Rev. B 113, 245422 – Published 22 June, 2026

DOI: https://doi.org/10.1103/l88j-p4f3

Abstract

Open-shell nanographenes offer a controlled setting to study correlated magnetism emerging from π-electron systems. Here, we study non-bipartite Fermi-Hubbard ladders describing oligo(indenoindene) molecules. These feature a gapped, weakly dispersing manifold of quasizero modes in their single-particle spectra, and we show that their low-energy properties can be effectively mapped onto an interacting set of spin-1/2 degrees of freedom. Using density matrix renormalization group simulations of the full Fermi-Hubbard model, we obtain their excitation spectra, entanglement profiles, and spin-spin correlations. We then construct optimized delocalized fermionic modes that act as emergent spins and demonstrate that their interactions are well described by a frustrated J1–J2 Heisenberg chain. This effective description clarifies how spin degrees of freedom arise and interact in non-bipartite nanographene ladders, providing a compact and accurate representation of their correlated behavior.

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Information

Phys. Rev. B 113, 245422– Published 22 June, 2026
  • Received 12 January 2026
  • Revised 27 April 2026
  • Accepted 3 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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