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TT: Fachverband Tiefe Temperaturen

TT 80: Correlated Electrons: Poster

TT 80.15: Poster

Thursday, March 21, 2024, 15:00–18:00, Poster E

Perturbative approach to the quantum phase transition in the Dicke-Ising chain — •Jonas Leibig, Anja Langheld, Max Hörmann, and Kai Phillip Schmidt — Department Physik, Staudtstraße 7, Friedrich-Alexander Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany

For the first time, we calculate high-order series expansions of the Dicke-Ising chain in the strong-coupling limit. We achieve this by applying a conditional displacement transformation and mapping to a self-consistent matter problem. We improve former results [1, 2] and are now able to derive the exact series results in the thermodynamic limit. We solve the self-consistent equations up to order 20 for ground-state energy and magnetization and analyze the phase diagram.

We examine ferromagnetic and antiferromagnetic Ising interactions, including the Dicke model and quantized transverse-field Ising chain as limiting cases. For ferromagnetic interactions, a second-order quantum phase transition occurs up to J = 0.5h from the Dicke limit and a first-order transition until J = 2h from the other limit. In the range between 0.5h and 2h, distinguishing between a first- and second-order phase transition is challenging. Quantum Monte Carlo simulations support the series approach, particularly for antiferromagnetic Ising interactions.

[1] J. Rohn et al., Phys. Rev. Res. 2, 023131 (2020)

[2] Y. Zhang et al., Sci Rep 4, 4083 (2014)

Keywords: Light-matter interaction; High-order series expansion; Dicke-Ising chain; Mean field