WEIRD BEHAVIOR IN QUANTUM DOTS. Interesting things happen when particles are confined in a tiny box. Researchers at MIT led by Raymond Ashoori (617-253-5585) make themselves such a box, a quantum dot, out of semiconductors---a layer of gallium arsenide between layers of aluminum gallium arsenide. On top of this sandwich sits a metal gate electrode which attracts electrons into the dot and controls the arrival or departure of electrons one at a time. Building up from just one electron, the MIT physicists collect a puddle of electrons and observe how the arrival of each newcomer must overcome (with the help of an increasing gate voltage) the mutual repulsion ("Coulomb blockade") of those already in place. For small dots (0.2 microns across) a graph of charge-vs-voltage would look like a staircase. Such an effect is at the heart of single-electron transistors (SET), which act as sensitive detectors of electrical charge (just as superconducting quantum interference devices---SQUIDS--- are sensitive detectors of magnetic flux). For larger dots (0.5-1.2 microns across), containing fewer than several hundred electrons, the MIT scientists were astonished to observe an unexpected and mysterious pairing: for each stepwise voltage increase not one but two electrons were able to join the puddle. The pairing has not yet been explained but the data strongly suggest that it arises from a novel quantum effect that develops whenever electrons are localized into spatially isolated regions within the dots. For medium-sized dots (0.5 microns) the physics gets even weirder: the pairing occurs only for every fourth or fifth electron. The goal now is to understand the underlying pairing mechanism. (Talk at last week's APS meeting in Los Angeles.)