Dynamical instability of a spin spiral in an interacting Fermi gas as a probe of the Stoner transition

Abstract

We propose an experiment to probe ferromagnetic phenomena in an ultracold Fermi gas, while alleviating the sensitivity to three-body loss and competing many-body instabilities. The system is initialized in a small pitch spin spiral, which becomes unstable in the presence of repulsive interactions. To linear order the exponentially growing collective modes exhibit critical slowing down close to the Stoner transition point. Also, to this order, the dynamics are identical on the paramagnetic and ferromagnetic sides of the transition. However, we show that scattering off the exponentially growing modes qualitatively alters the collective mode structure. The critical slowing down is eliminated and in its place a new unstable branch develops at large wave vectors. Furthermore, long-wavelength instabilities are quenched on the paramagnetic side of the transition. We study the experimental observation of the instabilities, specifically addressing the trapping geometry and how phase-contrast imaging will reveal the emerging domain structure. These probes of the dynamical phenomena could allow experiments to detect the transition point and distinguish between the paramagnetic and ferromagnetic regimes.

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Cited by in corpus (11)

• Universal spin dynamics in two-dimensional Fermi gases
• Far-from-equilibrium field theory of many-body quantum spin systems: Prethermalization and relaxation of spin spiral states in three dimensions
• Observation of the Leggett-Rice effect in a unitary Fermi gas
• Ferromagnetic spin correlations in a few-fermion system
• Itinerant ferromagnetism in an interacting Fermi gas with mass imbalance
• Spin segregation via dynamically induced long-range interaction in a system of ultracold fermions
• Itinerant ferromagnetism with finite ranged interactions
• Dynamical spin-flip susceptibility for a strongly interacting ultracold Fermi gas
• Quantum Monte Carlo study of the two-dimensional ferromagnet
• Non-Hermitian Ferromagnetism in an Ultracold Fermi Gas
• Itinerant ferromagnetism of a dipolar Fermi gas with Raman-induced spin-orbit coupling