Most materials exhibit slow fluctuations, with a broad distribution of characteristic rates, in a variety of electrical, mechanical, magnetic, and optical parameters. Despite the ubiquity of a simple form (1/f) for the frequency spectrum of such fluctuations, a wide variety of mechanisms are involved, as has been demonstrated in past experiments. These fluctuations are of interest for two general reasons. First, they limit the performance of a variety of sensors and devices. Second, they provide a useful tool to study fundamental properties of materials, especially the poorly understood types of materials known as glasses, which exhibit partially frozen random structures. They are using electrical, optical and magnetic fluctuation techniques to investigate ordinary glasses, glassy metals, spin glasses, magnetic materials with random domain structures, and other systems. Their particular focus is on how frozen random structures emerge from fluid random structures as temperature is lowered, and on what type of unfrozen modes remain at very low temperatures.
