151385 20251017144629.0 doi 10.1103/PhysRevB.111.035156 sideral 143087 ART-2025-143087 eng Román-Roche, Juan Universidad de Zaragoza (orcid)0000-0003-2995-6615 Linear response theory for cavity QED materials at arbitrary light-matter coupling strengths 2025 Access copy available to the general public Unrestricted We develop a linear response theory for materials collectively coupled to a cavity that is valid in all regimes of light-matter coupling, including symmetry-broken phases. We present and compare two different approaches. First, we use a coherent path-integral formulation for the partition function to obtain thermal Green's functions. This approach relies on a saddle-point expansion for the action that can be truncated in the thermodynamic limit. Second, we formulate the equations of motion for the retarded Green's functions and solve them. We use a mean-field decoupling of high-order Green's functions to obtain a closed, solvable system of equations. Both approaches yield identical results in the calculation of response functions for the cavity and material. These are obtained in terms of the bare cavity and material responses. In combination, the two techniques clarify the validity of a mean-field decoupling in correlated light-matter systems and provide complementary means to compute finite-size corrections to the thermodynamic limit. The theory is formulated for a general model that encompasses most of the systems typically considered in the field of cavity QED materials. Finally, we provide a detailed application of the theory to the quantum Hall effect and to a collection of spin models. info:eu-repo/grantAgreement/ES/AEI/CEX2023-001286-S info:eu-repo/grantAgreement/ES/DGA/E09-17R-Q-MAD info:eu-repo/grantAgreement/EUR/MICINN/TED2021-131447B-C21 info:eu-repo/semantics/openAccess by-nc-nd https://creativecommons.org/licenses/by-nc-nd/4.0/deed.es info:eu-repo/semantics/article info:eu-repo/semantics/acceptedVersion Gómez-León, Álvaro Luis Vitalla, Fernando (orcid)0000-0001-6284-0521 Zueco, David (orcid)0000-0003-4478-1948 2004 405 Universidad de Zaragoza Dpto. Física Teórica Área Física Teórica 111, 3 (2025), 035156 [21 pp.] Phys. Rev. B Physical Review B 2469-9950 2011399 http://zaguan.unizar.es/record/151385/files/texto_completo.pdf Postprint 3181230 http://zaguan.unizar.es/record/151385/files/texto_completo.jpg?subformat=icon icon Postprint oai:zaguan.unizar.es:151385 articulos driver 2025-10-17-14:25:47 ARTICLE