Number 358 (Story #1), February 11, 1998 by Phillip F. Schewe and Ben Stein SUPERCONDUCTIVITY-DEPENDENT FRICTION. A common parlor trick consists of yanking a tablecloth out from beneath an assortment of tableware. If you yank fast enough, the wineglasses remain where they are. At Northeastern University, this feat is acted out on a nanometer scale, with a thin (only one or two molecules thick) sliver of frozen nitrogen acting as the tableware, and a lead substrate as the tablecloth. Jacqueline Krim (617-373-2902) and her colleagues perform this kind of experiment in order to study friction at the atomic level. Despite the billion-dollar industrial importance of friction, it is still relatively little understood. In Krim's work a delicate quartz microbalance (with the lead substrate) is moved back and forth about 10 nm at rates of a million times per second, with the overlying nitrogen going along for the ride. With this approach the Northeastern researchers have measured what are probably the smallest frictional shear stresses yet seen (excepting only superfluids, which experience no friction). But a phenomenon even more interesting has emerged: when the lead substrate is chilled below its superconducting transition, the friction between the lead and the frozen nitrogen dramatically drops. This seems to represent a new and unexpected behavior of superconductors, and this has fascinated and puzzled theorists. (A. Dayo et al., upcoming article in Physical Review Letters.)