Charge transfer spin-polarons and ferromagnetism in weakly doped AB-stacked TMD heterobilayers

Abstract

We study the formation of ferromagnetic and magnetic polaron states in weakly doped heterobilayer transition metal dichalcogenides in the ``heavy fermion'' limit in which one layer hosts a dense set of local moments and the other hosts a low density of itinerant holes. We show that interactions among the carriers in the itinerant layer induces a ferromagnetic exchange. We characterize the ground state finding a competition, controlled by the carrier concentration and interlayer exchange, between a layer decoupled phase of itinerant carriers in a background of local moments, a fully polarized ferromagnet and a canted antiferromagnet. In the canted antiferromagnet phase the combination of the in-plane 120$^{\circ}$ N\'eel order and Ising spin orbit couplings induces winding in the electronic wavefunction giving rise to a topologically non-trivial spin texture and an observable anomalous Hall effect. At larger carrier density the ferromagnetically ordered phase transitions into a paramagnetic heavy Fermi liquid state. This theory enables a comprehensive understanding of the existing experimental observations while also making predictions including experimental signatures enabling direct imaging of spin polaron bound states with scanning tunneling microscopy. Our work shows that the prevailing paradigm of the (Doniach) phase diagram of heavy fermion metals is fundamentally modified in the low doping regime of heterobilayer transition metal dichalcogenides.