Mesoscopic Physics

Mesoscopic physics is a sub-discipline of condensed matter physics which deals with materials of an intermediate length scale. The scale of such materials can be described as being between the size of a quantity of atoms (such as a molecule) and of materials measuring micrometres. The lower limit can also be defined as being the size of individual atoms. At the micrometre level are bulk materials. Mesoscopic and macroscopic objects have in common that they both contain a large number of atoms. Whereas average properties derived from its constituent materials describe macroscopic objects, as they usually obey the laws of classical mechanics, a mesoscopic object, by contrast, is affected by fluctuations around the average, and is subject to quantum mechanics.

In other words, a macroscopic device, when scaled down to a meso-size, starts revealling quantum mechanical properties. For example, at the macroscopic level the conductance of a wire increases continuously with its diameter. However, at the mesoscopic level, the wire's conductance is quantized - the increases occur in discrete, or individual, whole steps. During research, mesoscopic devices are constructed, measured, and observed experimentally and theoretically in order to advance understanding of the physics of insulators, semiconductors, metals, and superconductors. The applied science of mesoscopic physics deals with the potential of building nano-devices.

Mesoscopic physics also addresses fundamental practical problems which occur when a macroscopic object is miniaturized, as with the miniaturization of transistors in semiconductor electronics. The physical properties of materials change as their size approaches the nanoscale, where the percentage of atoms at the surface of the material becomes significant. For bulk materials larger than one micrometre, the percentage of atoms at the surface is insignificant in relation to the number of atoms in the entire material. This sub-discipline has dealt primarily with artificial structures of metal or semiconducting material which have been fabricated by the techniques employed for producing microelectronic circuits.

There is no rigid definition for mesoscopic physics, but the systems studied are normally in the range of 100 nm (the size of a typical virus) to 1 000 nm (the size of a typical bacterium). 100 nanometers is the approximate upper limit for a nanoparticle. Thus mesoscopic physics has a close connection to the fields of nanofabrication and nanotechnology. Devices used in nanotechnology are examples of mesoscopic systems. Three categories of new phenomena in such systems are interference effects, quantum confinement effects, and charging effects.