Detection of a bosonic metallic state that breaks the $Z_2$ time-reversal symmetry has been recently reported in ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$ with a doping level $x\approx 0.8$. This is a metallic state of fermionic quadruplets that breaks time-reversal symmetry. As such, it has no condensed Cooper pairs but has a long-range order between fermionic quartets. In the present paper, we investigate the emergence of this phase in a two-component London model via Monte Carlo simulations as a function of various intercomponent couplings.

• Received 9 February 2022
• Revised 22 May 2022
• Accepted 10 June 2022

DOI:https://doi.org/10.1103/PhysRevB.105.214520

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Published by the American Physical Society