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arXiv:2606.11060

Interplay between photon condensation and electron-electron interactions in molecular systems

Matteo Parisi, Elisabetta Paladino, Giuseppe A. Falci, Gian Marcello Andolina, Salvatore Savasta, Marco Polini, Francesco M. D. Pellegrino

cond-mat.mes-hallcond-mat.str-elquant-phSubmitted Jun 9, 2026• Announced Jun 10, 2026

v1 · Jun 9, 2026 v2 · Oct 20, 2026

Abstract

We investigate a minimal molecular model consisting of square planar plaquettes hosting multiple electrons, whose dynamics is governed by a tight-binding Hamiltonian supplemented by on-site Hubbard repulsion. By coupling this system to a spatially nonuniform cavity mode, we analyze the emergence of a magnetostatic instability, namely photon condensation, originating from the paramagnetic Van Vleck mechanism. The global behavior of the system is analyzed for different electronic filling factors, and we find that, except for the special cases of half-filling and single electron, where the transition, if it occurs, is necessarily a second order phase transition, the global system may also undergo a first order transition because of the action of the electron-electron interaction. The polaritonic excitation energies are analyzed, providing clear spectroscopic signatures of the magnetostatic instability and of its order.

Journal reference: Phys. Rev. B 114, 225416 (2026)
DOI: 10.1103/7zlp-y14w
Comments: 22 pages, 8 figures

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