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First-order photon condensation in magnetic cavities: A two-leg ladder model
by Zeno Bacciconi, Gian Marcello Andolina, Titas Chanda, Giuliano Chiriacò, Marco Schiró, Marcello Dalmonte
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|Authors (as registered SciPost users):
|Gian Marcello Andolina · Zeno Bacciconi · Marcello Dalmonte
We consider a model of free fermions in a ladder geometry coupled to a nonuniform cavity mode via Peierls substitution. Since the cavity mode generates a magnetic field, no-go theorems on spontaneous photon condensation do not apply, and we indeed observe a phase transition to a photon condensed phase characterized by finite circulating currents, alternatively referred to as the equilibrium superradiant phase. We consider both square and triangular ladder geometries, and characterize the transition by studying the energy structure of the system, light-matter entanglement, the properties of the photon mode, and chiral currents. The transition is of first order and corresponds to a sudden change in the fermionic band structure as well as the number of its Fermi points. Thanks to the quasi-one dimensional geometry we scrutinize the accuracy of (mean field) cavity-matter decoupling against large scale density-matrix renormalization group simulations. We find that light-matter entanglement is essential for capturing corrections to matter properties at finite sizes and for the description of the correct photon state. The latter remains Gaussian in the the thermodynamic limit both in the normal and photon condensed phases.
Published as SciPost Phys. 15, 113 (2023)
Author comments upon resubmission
We thank you for handling our manuscript, and the Referees for their insightful reports. We have addressed the Referees comments and suggestions in the new version of the manuscript. Below, as well as in the comments in reply to the Referees' reports, please find a list of changes.
List of changes
- Addition of Ref.  and of a sentence in the introduction (section 1) that explains it. Slight modification of the last paragraph in section 2 where Ref  is discussed again in the context of experimental relevance of the considered model
- Addition of Ref. [8,11] as suggested by Referee 2
- Addition of a clearer discussion in the introduction (section 1, 4th paragraph) and in the conclusions (section 5, 1st paragraph) on the necessity of a magnetic coupling to evade no-go theorems.
- Rephrasing of the sentence cited by Referee 3 (section 3.2, paragraph Magnetostatic instability) and addition of Ref. 
Submission & Refereeing History
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