Number 65, January 24, 1992 by Phillip F. Schewe and Ben Stein D-WAVE ELECTRON PAIRS may have been observed in cuprate superconductors. In the BCS theory, superconductivity is thought to come about when electrons pair off into Cooper pairs. The relative orbital angular momentum of the pair can have a value of 0 ("s-wave"), 1 (p-wave), 2 (d-wave), and so forth. Cooper pairs are commonly in s-wave states. In certain "heavy-electron" materials (containing uranium) superconductivity may be p-wave in nature. Now evidence for d-wave superconductivity comes in the form of NMR studies of the copper nuclei in high-temperature superconductivity. In the 3 Feb. issue of Physical Review Letters, three articles are devoted to this subject. A group from the University of Illinois (J. A. Martindale et al.; contact Charles Slichter at 217-333-3834) and a Iowa State/Pavia (Italy) collaboration (Ferdinando Borsa et al.) report experimental results, while a theoretical analysis is presented by Nejut Balut and Douglas Scalapino at UC Santa Barbara. EXPLOITING MECHANICAL STRAIN EFFECTS IN SEMICONDUCTORS has allowed researchers to achieve some of the latest advances in laser design. In the newest models, light is released from ultra-thin, nanometer-scale junctions known as "quantum wells." Compared to the thicker junctions made in the past, quantum wells can better tolerate the surface strain which arises when the atoms in the well layer have different atomic spacings from those in the surrounding p- and n-semiconductor layers. As a result, scientists can vary materials in the junctions to a greater degree than ever before, bringing about a much wider variety of energies in semiconductor lasers. Straining techniques in quantum wells led to the first semiconductor lasers in the green range (New Scientist, 11 Jan.1992). In addition, the fastest laser yet, a gallium-arsenide-based laser which turns on and off 28 billion times a second, appears to have resulted from straining effects on the Ga-As lattice produced by a Ga-In-As quantum well. (Science News, 11 Jan.1992) STRUCTURALLY DISTINCT COUSINS OF FULLERENES have been hypothesized by two research teams working independently. The proposed structures, C-168 "buckygyms" (a Rutgers-IBM team) and C-216 "schwarzite" (a Cornell-Corning team), would form from flat graphite sheets, as is the case with fullerenes, but the sheets would contain 7-atom carbon rings instead of 5-atom rings. Whereas the presence of the 5-fold rings in the growing graphitic sheet causes it to curl "positively" into the closed spheres we know as Buckyballs, the 7-fold carbon rings would cause the proposed clusters to fold "negatively," contorting locally into saddlelike shapes and forming an infinite cagelike structure (the large-scale structure of C-168 would be similar to diamond, but with a unit cell 100 times bigger). The C-168 researchers predict that the material would have elastic constants similar to those of silicon but with half the density of graphite, making for a lightweight, durable structure. The C-216 designers predict that their structure would be more energy efficient than fullerenes; the C-168 researchers make the same prediction. No one has found these structures, but the C-216 researchers say that they may already be made with fullerenes in conventional carbon-arc setups. (C-168: Vanderbilt et al., 27 Jan. Physical Review Letters; contact Jerry Tersoff of IBM, 914-945-3138; C-216: Lenosky et al., 23 Jan. 1992 issue of Nature).