The
Quantum-Hall Effect
Liquid to Insulator Transition
The figure above is a typical example of a moderately high-quality two-dimensional GaAs sample. The curves shown are magnetic field (B) traces of the longitudinal resistivity obtained at very low temperatures (25 mK for the blue trace, and progressively higher temperatures going all the way to 280 mK for the red curve). The apparent random fluctuations of the resistivity are nothing but the famous fractional quantum Hall effect discovered in 1982 by Dan Tsui and his collaborators at Bell labs. These 'fluctuations' are far from being random. They are extremely regular and reproducible and are, in fact, periodic in 1/B. Associated with the deep minima of the resistivity (it actually approaches zero, as in superconductors!) are plateaus in the Hall resistivity (removed for clarity in this graph, but can be seen here). The focus of my research in the past few years was the study of the termination of the QHE series, where the system undergoes a QH-insulator transition (click on graph for more details).