Regensburg 2022 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 34: Correlated Electrons: Theory 2

TT 34.7: Talk

Thursday, September 8, 2022, 16:30–16:45, H23

Cavity-induced long-range interactions in strongly correlated systems — •Paul Fadler¹, Jiajun Li², Kai Phillip Schmidt¹, and Martin Eckstein¹ — ¹Friedrich-Alexander-Universität Erlangen-Nürnberg — ²Paul Scherrer Institut

In recent years, the coupling of optical cavity modes to solid states systems has emerged as a possible way to control material properties. Here we investigate cavity-induced long-range interactions between spins in a Mott insulator, which are a new feature of the coupling to the quantized cavity field, and are absent in a control of magnetism by classical light. In detail, for the Fermi-Hubbard model at half filling we show that the cavity coupling leads to long-range four-spin terms in the effective low spin model at large onsite interaction U, in addition to the conventional antiferromagnetic Heisenberg exchange interaction.

To obtain these long-range interactions, we compare exact diagonalization, a perturbative approach based on the effective spin-photon Hamiltonian description of the system, and fourth-order perturbation theory in the Hubbard model. We show that the phenomenologically motivated spin-photon Hamiltonian fails to describe the interactions properly close to resonances of the cavity and charge excitations. It is therefore not possible to perturbatively treat cavity coupled correlated systems in an effective spin basis.