Itinerant spin polaron and magnetic states in semiconductor moiré superlattices

We study the instability of the ferromagnetic ground state of moiré TMD heterobilayers in magnetic field, which we model by the Hubbard model on triangular lattice. In strong interaction regime, we find a drastic difference between the charge e and -e excitations of the spin-polarized Mott insulator occurring in a wide range of magnetic fields below the saturation field h_s~t>>J. In the limit U = inf, we find an exact solution for a hole spin polaron which leads to a magnetic instability at h~t. The hole spin polaron is an itinerant bound state of a spin flip and a hole in a fully polarized background, which has spin-3/2 and binding energy ε_b~t and forms due to a purely kinetic origin. The charge-e excitation is simply a doublon. The saturation field h_s~ t for finite hole doping is much larger than that for electron doping, where h_s~J<at small electron doping and decreases further due to the emergence metallic magnetism. We propose experimental signatures which will allow to unambiguously reveal the presence of the hole spin polaron physics and address the existing observations.