Valley polarization transition in a two-dimensional electron gas

TL;DR

This paper theoretically investigates whether the observed resistivity change in a 2D electron gas aligns with a spontaneous valley-polarization transition from two to one valley, confirming the experimental claim through transport analysis.

Contribution

It provides a theoretical validation that the experimentally observed resistivity change is consistent with a spontaneous valley-polarization transition in a 2DEG.

Findings

Resistivity change matches the valley polarization transition

The transition occurs at a critical carrier density

Transport signatures support the phase transition hypothesis

Abstract

We theoretically study transport signatures associated with a spontaneous 2-valley to 1-valley quantum phase transition in a two-dimensional electron gas (2DEG) tuned by decreasing the 2D carrier density, as claimed in a recent experiment [Phys. Rev. Lett. 127, 116601 (2021)]. The key issue we focus on is whether the experimentally measured 2D resistivity as a function of carrier density is consistent (or not) with an underlying spontaneous valley-polarization transition as assumed uncritically in the experimental report. Our theoretical analysis is particularly germane since the experiment does not directly measure the change in the Fermi surface resulting from the valley polarization transition, but infers such a transition indirectly through transport measurements. We validate the experimental claim, showing that indeed the observed sudden change in the 2D resistivity is quantitatively consistent with a sudden change in the valley polarization from 2 to 1 at the critical density.