Saturation of Spin-Polarized Current in Nanometer Scale Aluminum Grains

TL;DR

This study investigates how spin-polarized current saturates in nanometer-scale aluminum grains, revealing that spin relaxation is primarily governed by spin-orbit interaction and occurs at rates comparable to electron tunneling.

Contribution

It provides the first detailed measurement of spin relaxation rates in aluminum grains and links these rates to spin-orbit interaction using the Elliot-Yafet scaling.

Findings

Spin-polarized current saturates at high bias voltages.

Spin relaxation rate is comparable to tunneling rate.

Spin relaxation governed by spin-orbit interaction.

Abstract

We describe measurements of spin-polarized tunnelling via discrete energy levels of single Aluminum grains. In high resistance samples ($\sim G\Omega$), the spin-polarized tunnelling current rapidly saturates as a function of the bias voltage. This indicates that spin-polarized current is carried only via the ground state and the few lowest in energy excited states of the grain. At the saturation voltage, the spin-relaxation rate $T_1^{-1}$ of the highest excited states is comparable to the electron tunnelling rate: $T_1^{-1}\approx 1.5\cdot 10^6 s^{-1}$ and $10^7s^{-1}$ in two samples. The ratio of $T_1^{-1}$ to the electron-phonon relaxation rate is in agreement with the Elliot-Yafet scaling, an evidence that spin-relaxation in Al grains is governed by the spin-orbit interaction.