Observation of spin Coulomb drag in a two-dimensional electron gas

TL;DR

This paper experimentally demonstrates that in a two-dimensional electron gas, spin current is significantly affected by electron-electron interactions, challenging previous assumptions that spin transport is unaffected by such interactions.

Contribution

The study provides the first experimental evidence that spin Coulomb drag influences spin transport in a 2D electron gas, revealing a new aspect of spin dynamics.

Findings

Spin Coulomb drag affects spin current in 2D electron gases.

Electron-electron collisions control spin flow over various conditions.

Contradicts the assumption that spin current is unaffected by e-e interactions.

Abstract

An electron propagating through a solid carries spin angular momentum in addition to its mass and charge. Of late there has been considerable interest in developing electronic devices based on the transport of spin, which offer potential advantages in dissipation, size, and speed over charge-based devices. However, these advantages bring with them additional complexity. Because each electron carries a single, fixed value (-e) of charge, the electrical current carried by a gas of electrons is simply proportional to its total momentum. A fundamental consequence is that the charge current is not affected by interactions that conserve total momentum, notably collisions among the electrons themselves. In contrast, the electron's spin along a given spatial direction can take on two values, "up" and "down", so that the spin current and momentum need not be proportional. Although the transport of spin polarization is not protected by momentum conservation, it has been widely assumed that, like the charge current, spin current is unaffected by electron-electron (e-e) interactions. Here we demonstrate experimentally not only that this assumption is invalid, but that over a broad range of temperature and electron density, the flow of spin polarization in a two-dimensional gas of electrons is controlled by the rate of e-e collisions.