New shards of electron charge found.

When electrons get together, strange things can happen. Physicists have long suspected, for instance, that electrons can clump into composite particles, known as quasiparticles, each with a third or less of the electric charge of a single electron. These composites had been expected to appear when ultracold electrons are flowing within an extremely thin layer between two slabs of semiconductor and, in addition, a powerful magnetic field cuts through the layer.

Two years ago, Israeli and French scientific teams independently demonstrated the existence of quasiparticles with one-third charges. Now in the May 20 NATURE, the Israeli team, located at the Weizmann Institute of Science in Rehovot, reports also bagging evidence for quasiparticles with one-fifth charges.

In all the cases, the scientists determined quasiparticle charge by analyzing the electrical noise created when quasiparticle currents funneled through very narrow regions of the thin layers.

"To observe these unusual creatures, you need unusual circumstances," says Raft de Picciotto, a member of the Israeli team who is now at Lucent Technologies' Bell Labs in Murray Hill, N.J.

Studies of electric flows under similar circumstances created a huge sensation in physics 17 years ago. Physicists had long known that the presence of a magnetic field perpendicular to the thin layer creates a sideways current, a phenomenon known as the Hall effect. They had also determined that, at very low temperatures, the electrical resistance to that current increases in steps proportional to the charge of the electron.

Then in 1982, Daniel C. Tsui of Princeton University and Horst L. Stormer, now at Columbia University, made the puzzling discovery that there are additional resistance steps, which are proportional to fractional charges. To explain them, Robert B. Laughlin, who is now at Stanford University, came up with a theory involving quasiparticles. The three scientists won the Nobel Prize in Physics last year for their findings (SN: 10/17/98, p. 247).

De Picciotto says that the new results support Laughlin's predictions. Many quasiparticle partial charges form, equal to certain fractions with odd denominators, but they don't always directly correspond to the fractional resistance steps.