APS Medal for Exceptional Achievement in Research (2020): The Metal-Insulator Transition in Strongly Interacting Electron Systems in Two Dimensions**

It is a great pleasure to be given this opportunity to celebrate and thank the American Physical Society for selecting me to receive last year’s 2020 APS Medal for Exceptional Achievement in Research for “fundamental contributions to the physics of electronic transport in solids and molecular magnetism”. While my interest in molecular magnets began some twenty five years ago, various issues concerning electronic transport have spanned my entire research career. Starting with early work in the 1960’s on the resistance minimum and what is now known as the Kondo effect, my investigations of different aspects concerning electrical transport have continued through the years via studies of the metal-insulator transition (MIT) in doped semiconductors, measurements of the critical conductivity exponents at the MIT associated with various universality classes, hopping conduction and the Coulomb gap, the roles of disorder and interactions, and more. My most recent focus has been on the MIT in strongly interacting electron systems in two dimensions, where metallic behavior was not expected to occur. Here I will briefly summarize the current situation concerning this unresolved problem, and I will report exciting new experimental results that raise questions and open new doors for further research.