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Q: Fachverband Quantenoptik und Photonik

Q 5: Collective Effects and Disordered Systems

Q 5.2: Vortrag

Montag, 10. März 2025, 11:15–11:30, HS I PI

Melting of Devil’s staircases in the long-range Dicke-Ising model — •Jan Alexander Koziol and Kai Phillip Schmidt — Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Staudtstraße 7, 91058 Erlangen, Germany

We present ground-state phase diagrams of the antiferromagnetic long-range Ising model under a linear coupling to a single bosonic mode on the square and triangular lattice. In the limit of zero coupling the ground state magnetization forms a Devil’s staircase structure of magnetization plateaux as a function of an applied longitudinal field in Ising direction. The linear coupling to a single bosonic mode melts this structure to a so-called superradiant phase with a finite photon density in the ground state. The long-range interactions lead to a plethora of intermediate phases that break the translational symmetry of the lattice, as well as having a finite photon density. To study the ground-state phase diagram we apply an adaption of the unit-cell-based mean-field calculations [1,2], which capture all possible magnetic unit cells up to a chosen extent. Further, we exploit a mapping of the non-superradiant phases to the Dicke model in order to calculate upper bounds for phase transitions towards superradiant phases [3]. In the case of second-order phase transitions, these bounds agree with the boundaries determined by the mean-field calculations.

[1] J. A. Koziol et al., SciPost Phys. 14, 136 (2023)

[2] J. A. Koziol et al., SciPost Phys. 17, 111 (2024)

[3] A. Schellenberger et al., SciPost Phys. Core 7, 038 (2024)

Keywords: Dicke-Ising model; long-range interactions; light-matter coupling; Devil's staircase; magnetization plateaux