Electron-Electron Interactions and the Metal-Insulator Bifurcation in 2D

Transport properties of extremely high purity two-dimensional (2D) electron systems at low temperatures are still not well understood either experimentally or theoretically, even though these systems are very important in modern computing devices. An important issue is the mechanism behind the sudden change in the temperature dependence of the resistivity observed at low but non-zero temperatures. This phenomenon is of interest whether or not there is an actual transition in the limit of zero temperature. We have found direct evidence of the role of the Coulomb repulsion and exchange between electrons in this phenomenon. We identify a relationship between the strength of an external magnetic field parallel to the electron plane and the critical density at the bifurcation which depends on properties of the 2D electron-electron correlation function. This points to Coulomb repulsion and exchange playing a central role in driving the bifurcation.