We investigate the behavior of the collective excitations of adsorbed ${}^4\mathrm{He}$ in an ordered hexagonal mesopore, examining the crossover from a thin film to a confined fluid. Here, we present the inelastic scattering results as a function of filling at constant temperature. We find a monotonic transition of the maxon excitation as a function of filling. This has been interpreted as corresponding to an increasing density of the adsorbed helium, which approaches the bulk value as filling increases. The roton minimum exhibits a more complicated behavior that does not monotonically approach bulk values as filling increases. The full pore scattering resembles the bulk liquid accompanied by a layer mode. The maxon and roton scattering, taken together, at intermediate fillings does not correspond to a single bulk liquid dispersion at negative, low, or high pressure.

• Received 16 February 2018
• Revised 10 April 2018
• Corrected 29 May 2018

DOI:https://doi.org/10.1103/PhysRevB.97.184511