False Vacuum Decay in Flat-Band Ferromagnets: Role of Quantum Geometry and Chiral Edge States

Dynamical control of quantum matter is a challenging, yet promising direction for probing strongly correlated states. Motivated by recent experiments in twisted MoTe$_2$ that demonstrated optical control of magnetization, we propose a protocol for probing magnetization dynamics in flat-band ferromagnets. We investigate the nucleation and dynamical growth of magnetic bubbles prepared on top of a false vaccum in both itinerant ferromagnets and spin-polarized Chern insulators. For ferromagnetic metals, we emphasize the crucial role of a non-trivial quantum geometry in the magnetization dynamics, which in turn also provides a probe for the quantum metric. Furthermore, for quantum Hall ferromagnets, we show how properties of chiral edge modes localized at domain-wall boundaries can be dynamically accessed. Our work demonstrates the potential for nonequilibrium protocols to control and probe strongly correlated phases, with particular relevance for twisted MoTe$_2$ and graphene-based flat-band ferromagnets.

💡 Research Summary

The authors propose and theoretically analyze a nonequilibrium protocol to study false‑vacuum decay in two‑dimensional flat‑band ferromagnets. Building on recent optical control of magnetization in twisted MoTe₂, they suggest preparing a metastable Ising‑type ferromagnetic state (the “false vacuum”) by applying a weak out‑of‑plane magnetic field Bz that slightly favors one spin orientation. A circularly polarized laser pulse then flips the magnetization in a finite region, creating a magnetic bubble of opposite polarization (the “true vacuum”). With Bz turned off, the two spin states are degenerate and the bubble either shrinks or expands depending on the competition between bulk energy gain Δf≈gμB Bz and the cost of a domain‑wall surface tension σ.

Using a phenomenological Landau‑Ginzburg free energy f