Spin-valley phase diagram of the two-dimensional metal-insulator transition

TL;DR

This study maps out a phase diagram for a 2D electron system in AlAs, showing how spin and valley polarization influence the metal-insulator transition, highlighting their equivalent roles.

Contribution

It introduces a method to independently control spin and valley degrees of freedom to explore their combined effects on the 2D metal-insulator transition.

Findings

Insulating phase occurs when both spin and valley are polarized.

Spin and valley degrees of freedom play equivalent roles in the transition.

Phase diagram maps the conditions for metallic and insulating states.

Abstract

Using symmetry breaking strain to tune the valley occupation of a two-dimensional (2D) electron system in an AlAs quantum well, together with an applied in-plane magnetic field to tune the spin polarization, we independently control the system's valley and spin degrees of freedom and map out a spin-valley phase diagram for the 2D metal-insulator transition. The insulating phase occurs in the quadrant where the system is both spin- and valley-polarized. This observation establishes the equivalent roles of spin and valley degrees of freedom in the 2D metal-insulator transition.