Physics Today

Few superconducting materials have presented us with the structural elegance and complexity displayed by the recently discovered high-Tc copper oxides. The structures of these materials, consisting of metal-oxygen layers stacked in a variety of sequences, with the metal atoms often in unusual coordinations, are interesting in their own right. More importantly, our present understanding of the properties of the oxide superconductors depends heavily on a knowledge of their structures.

While physical sciences deal with the interactions of matter and energy, economics can be said to deal with the production and exchange of goods and services. Because goods and services incorporate matter and energy, the physical sciences are clearly relevant to economics. In particular, one can expect the laws of thermodynamics to impose constraints on economic processes as they do on physical processes (figure 1). It is clear that the laws of conservation—of matter and energy, for example—have implications for the use of resources and for the generation and treatment of wastes. The law of the increase of entropy—the second law of thermodynamics—constrains economic processes to those that reduce available work, increasing the entropy of the Universe.

Conduction electrons in real crystalline solids behave very much like electrons in free space, moving in straight lines between collisions when subject to an electric field. But in an ideal (although cold) world, free from scattering by impurities, imperfections and thermal vibrations of the lattice, how would conduction electrons behave? That question, answered in principle long ago in light of the then newly developed quantum mechanics, was purely academic until recently.

Band-structure engineering has led to a fundamentally new laser with applications ranging from highly sensitive trace-gas analysis to communications.

Boron-rich molecules and solids hold a special place within chemistry. They do not follow the general bonding rules we are taught in chemistry classes. For example, some boron-rich solids are composed of 12-atom clusters of boron atoms in which each boron atom resides on a vertex of an icosahedron. These solids are very stable refractory materials with melting temperatures up to 2400 °C—a thousand degrees greater than silicon's. Beyond this, they possess numerous novel structural, electronic and thermal properties that are not only interesting but useful.

Interactions between electromagnetic waves and the most energetic ions in a plasma can perturb the orbits of those ions enough to expel them from the confining magnetic field.

Shampoos, paints, cements, and soft body armor that stiffens under impact are just a few of the materials whose rheology is due to the change in viscosity that occurs when colloidal fluids experience shear stress.

New techniques promise better forecasting of where damaging contaminants in the ocean or atmosphere will end up.