Layer-Controlled Intermolecular Coupling and Many-Body Effects in C60 Films.

Crystalline C60 is a molecular solid whose electronic properties emerge from the interplay of intermolecular hopping, electron correlations, and electron-vibration coupling. Unlike moiré van der Waals heterostructures, where the interaction strength is commonly tuned by twist angle, molecular materials offer a complementary route in which the layer number, molecular orientation, and substrate registry provide experimentally accessible control parameters. Here we present a systematic thickness-dependent angle-resolved photoemission study of C60 films, spanning the monolayer to the bulk limit. The HOMO-derived band exhibits a nonmonotonic evolution: the intermediate-thickness film shows a larger bandwidth, a reduced effective mass, and a pronounced gap-like and sub-band features. The experimental trends, together with Holstein-model simulations, point to strengthened effective intermolecular electronic coupling and enhanced electron-phonon-induced spectral renormalization in the intermediate-thickness regime. These results identify a dimensional crossover in C60 films and establish the layer number as an effective knob for engineering electronic structure and many-body interactions in molecular thin films.