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arXiv · 1812.01098

Antiferromagnetic self-ordering of a Fermi gas in a ring cavity

Elvia Colella·Stefan Ostermann·Wolfgang Niedenzu·Farokh Mivehvar·Helmut Ritsch
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Abstract

We explore the density and spin self-ordering of driven spin-$1/2$ collisionless fermionic atoms coupled to the electromagnetic fields of a ring resonator. The two spin states are two-photon Raman-coupled via a pair of degenerate counterpropagating cavity modes and two transverse pump fields. In this one-dimensional configuration the coupled atom-field system possesses a continuous $U(1)$ translational symmetry and a discrete $\mathbf{Z}_2$ spin inversion symmetry. At half filling for sufficiently strong pump strengths, the combined $U(1)\times \mathbf{Z}_2$ symmetry is spontaneously broken at the onset of a superradiant phase transition to a state with self-ordered density and spin structures. We predominately find an antiferromagnetic lattice order at the cavity wavelength. The self-ordered states exhibit unexpected positive momentum pair correlations between fermions with opposite spin. These strong cavity-mediated correlations vanish at higher pump strength.

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Elvia Colella, Stefan Ostermann, Wolfgang Niedenzu, Farokh Mivehvar, Helmut Ritsch. 2019-05-02. Antiferromagnetic self-ordering of a Fermi gas in a ring cavity. https://doi.org/10.1088/1367-2630%2Fab151e

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