  Electronic charge rearrangement between components of a heterostructure is
the fundamental principle to reach the electronic ground state. It is
acknowledged that the density of states distribution of the components governs
the amount of charge transfer, but a notable dependence on temperature has not
yet been considered, particularly for weakly interacting systems. Here, we
experimentally observe that the amount of ground state charge transfer in a van
der Waals heterostructure formed by monolayer MoS2 sandwiched between graphite
and a molecular electron acceptor layer increases by a factor of three when
going from 7 K to room temperature. State-of-the-art electronic structure
calculations of the full heterostructure that account for nuclear thermal
fluctuations reveal intra-component electron-phonon coupling and
inter-component electronic coupling as the key factors determining the amount
of charge transfer. This conclusion is rationalized by a model applicable to
multi-component van der Waals heterostructures.
