Thickness dependence of the ground-state properties in thin films of the heavy-fermion compound CeCu₆

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High-quality thin polycrystalline films of the heavy-fermion compound CeCu₆ were prepared by sputter deposition. The thicker of these films (with thickness up to around 200 nm) reproduce the properties of the bulk compound CeCu₆. As the thickness of the films is decreased, our measurements display strong deviations from the bulk properties, namely, a suppression of the heavy-fermion state. We show that possible `external' effects, like disorder, oxidation and morphology can be excluded and that this size effect is therefore an intrinsic property of CeCu₆. In addition, we investigate possible scenarios explaining the size effect, and find that the proximity of CeCu₆ to a quantum phase transition can account for this striking result.