Two‐Dimensional Electron Gases Continue to Exhibit Intriguing Behavior

The startling discoveries of the integral and fractional quantum Hall effects were made in two‐dimensional electron gases subjected to very high magnetic fields (see the story on page 17). Now, it appears, other surprises await us at lower fields. In a recent study, the longitudinal resistivity exhibited a strong anisotropy in a certain range of temperature and magnetic field: When plotted as a function of the magnetic field, the resistivity has a dip when the current flows in one direction and a strong peak when it flows in an orthogonal direction. There's no a priori reason to think that these two directions are different.