The presence of free spins in granular Al films is directly demonstrated by μSR measurements. A Mott transition is observed by probing the increase of the spin-flip scattering rate of conduction electrons as the nano-size metallic grains are being progressively decoupled. Analysis of the magneto-resistance in terms of an effective Fermi energy shows that it becomes of the order of the grains electrostatic charging energy at a room temperature resistivity ρ≈50,000μΩcm, at which a metal to insulator transition is known to exist. As this transition is approached the magneto-resistance exhibits a Heavy-Fermion like behavior, consistent with an increased electron effective mass.
@article{arxiv.1407.7467,
title = {Mott transition in granular aluminum},
author = {N. Bachar and S. Lerer and S. Hacohen-Gourgy and B. Almog and H. Saadaoui and E. Morenzoni and G. Deutscher},
journal= {arXiv preprint arXiv:1407.7467},
year = {2015}
}