Tunable heavy fermions in a moiré Kondo lattice

The formation of heavy electrons by merging a lattice of local magnetic moments to a sea of itinerant electrons is a profound problem in condensed matter physics. The emergence of moiré materials provides a new platform to explore this problem in simple and tunable fashions. Here we report the realization of a tunable Kondo lattice in AB-stacked MoTe₂/WSe₂ moiré bilayers. Heavy electrons are formed when the MoTe₂ layer is tuned to a strongly correlated Mott insulator, which supports a triangular lattice of local magnetic moments, and the WSe₂ layer is doped with itinerant carriers. Over ten-fold enhancement in the electron mass is observed when the itinerant carriers and local moments form Kondo singlets. The Kondo singlets can be destroyed by an external magnetic field; a sharpened destruction at low temperatures suggests the presence of quantum criticality. Our study lays the foundation for exploring the Doniach phase diagram in semiconductor moiré materials.