Probing Itinerant Magnetism in a Dipolar Lattice Gas

 

Itinerant magnetism, driven by the interplay of magnetism and transport, connects key phenomena such as superconductivity, quantum magnetism, and superfluidity. Spinor Bose–Einstein condensates provide an ideal platform to explore this interplay, where Bose enhancement favors ferromagnetism while lattice confinement can disrupt it. We study the dynamics of transverse magnetization in a gas of bosonic chromium atoms across the superfluid–Mott insulator transition in a 3D optical lattice. In the superfluid regime, ferromagnetic order persists, but increasing lattice depth suppresses spin currents, leading to a dynamical instability near the phase transition boundary. In the insulating regime, we derive effective spin models with dipolar and contact superexchange terms. We introduce a tractable spin-1 simplified model that elucidates the underlying physics, as well as a full analysis of the spin-3 dynamics . We also obtain short-time analytic expressions of the magnetization that reproduce the experimental observations. Our combined experimental and theoretical analysis provides new tools and insights into itinerant dipolar magnetism in optical lattices.