Phonon-engineered Nb film as a Mott-insulating tunnel-junction network

Herein, phonon engineering is applied to a metal. Suppressed phonon branches are expected to enhance electron–phonon interactions in metals. Independent resistance and magnetization measurements have confirmed the Mott transition, which has never been observed in pure, undoped metals. By repeatedly cooling and warming a periodically pierced Nb film, narrow Nb bridges left between adjacent thru-holes are converted to Mott-insulating bridges. The continuum in which these Mott-insulating bridges connect adjacent metallic Nb islands forms a tunnel-junction network, which can be used to implement a massively integrated single-electron device.