Apparent charge reduction in multipolarons crafted one-by-one in monolayer CrBr.

Manipulating electrons opens up emerging synthetic strategies. Multipolaron, as a rare quasiparticle containing multiple excess charges collectively dressed with shared local lattice distortions, provides an ideal medium for electron manipulation, yet remains elusive. Here, with scanning tunneling microscopy, we realize electron multipolarons in monolayer CrBr. The multipolaron is crafted via assembling single monopolarons with the tip, allowing their electron numbers to increase one-by-one controllably. With added electrons, the multipolaron exhibits stronger local band bending and upward shift of the polaronic states. Notably, the apparent charge of the multipolaron can be reduced by tip manipulation. First principles calculations reveal that the multipolaron is stabilized by large diffusion barriers and screening of the substrate. The apparent charge reduction is attributed to the formation of the polaron-exciton droplet where the multipolaron captures holes from the substrate to partially offset the Coulomb repulsion. Our findings establish an approach for studying polaron interactions at the atomic limit.