Kubo spins in nano-scale aluminum grains: A muon spin relaxation study

TL;DR

This study uses muon spin relaxation to investigate quantum size effects in nano-scale aluminum grains, revealing the presence of Kubo spins and their dependence on metallicity and temperature.

Contribution

It provides experimental evidence for Kubo spins in aluminum nanograins and links their behavior to quantum size effects and electron parity.

Findings

Relaxation rates indicate single electron spins in odd-electron grains.

Temperature dependence follows an activation law matching level splitting.

Weakly metallic films show smaller, faster-decreasing relaxation rates.

Abstract

We report muon spin relaxation rate measurements on films composed of aluminum grains having a size of a few nm, with a large energy level splitting of the order of 100 K. The films range from weakly metallic to insulating. In the insulating case the low temperature relaxation rate is consistent with the presence of single electron spins in grains having an odd number of electrons. The relaxation rate temperature dependence follows an activation law having an energy scale in agreement with the average level splitting. In weakly metallic films the relaxation rate is smaller and decreases faster with temperature. Overall our observations are in line with the presence of a Kubo spin in Al nano-size grains due to quantum size effects.