Dependence of Effective Mass on Spin and Valley Degrees of Freedom

TL;DR

This study investigates how the effective mass of 2D electrons in AlAs quantum wells varies with spin and valley polarization, revealing mass enhancement and insulating behavior under certain conditions.

Contribution

It provides experimental insights into the dependence of effective mass on spin and valley degrees of freedom in 2D electron systems.

Findings

Effective mass is enhanced when electrons are not fully spin and valley polarized.

Fully polarized electrons exhibit insulating behavior.

Mass enhancement depends on the degree of polarization.

Abstract

We measure the effective mass (m*) of interacting two-dimensional electrons confined to an AlAs quantum well while we change the conduction-band valley occupation and the spin polarization via the application of strain and magnetic field, respectively. Compared to its band value, m* is enhanced unless the electrons are fully valley and spin polarized. Incidentally, in the fully spin- and valley-polarized regime, the electron system exhibits an insulating behavior.