Basic properties

The recent observations of persistent currents in small metallic rings by Lévy et al. (1990), Chandrasekhar et al. (1991), and Mailly, Chapelier, and Benoit (1993) have opened a new field of research. Although small mesoscopic systems have been under intensive study for quite a long time, they have usually been studied by making contacts with metallic leads. As a result, one could obtain a finite conductance of the system that corresponded to a finite current in the presence of a finite voltage only. The experiments by Lévy et al. (1990) and by Chandrasekhar et al. (1991) were carried out in such a way that the metallic rings remained isolated. A slowly varying magnetic field was applied and a magnetic response was measured. In this situation it became possible to observe persistent currents in quite dirty samples in which the elastic mean free path l was much shorter than the circumference L. The existence of the persistent current is possible in isolated rings only, and Mailly, Chapelier, and Benoit (1993) demonstrated how the value of the persistent current decreases when increasing a weak coupling to leads.

The intriguing question of persistent currents in metal rings enclosing a magnetic flux was discussed in the 1960s by Byers and Yang (1961), F. Bloch (1965, 1968, 1970), Schick (1968), Gunter and Imry (1969).