A metal-insulator transition in 2D: Established facts and open questions

TL;DR

This paper reviews the discovery and ongoing debate about the metal-insulator transition in two-dimensional electron systems, emphasizing the role of strong interactions and highlighting unresolved questions in the field.

Contribution

It synthesizes experimental findings on 2D MITs and discusses the contrast with traditional theories, emphasizing the impact of electron interactions.

Findings

Experimental evidence of metallic states in 2D systems

Significant electron interactions influence the MIT

Many open questions remain in understanding 2D MITs

Abstract

The discovery of a metallic state and a metal-insulator transition (MIT) in two-dimensional (2D) electron systems challenges one of the most influential paradigms of modern mesoscopic physics, namely, that "there is no true metallic behavior in two dimensions". However, this conclusion was drawn for systems of noninteracting or weakly interacting carriers, while in all 2D systems exhibiting the metal-insulator transition, the interaction energy greatly exceeds all other energy scales. We review the main experimental findings and show that, although significant progress has been achieved in our understanding of the MIT in 2D, many open questions remain.