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

Abstract 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.