Coherent quantum phenomena in mesoscopic metallic conductors (Review Article)

Abstract

Quantum coherent phenomena in mesoscopic cylindrical metallic conductors are examined. When pure doubly- and singly-connected normal samples are placed in a longitudinal magnetic field, interference phenomena occur which depend on the magnetic flux through the cross-section of the conductor. The period of the induced oscillations is given by the quantum of flux, hc∕e, of the normal metal. Quantum states are formed in these structures by electron collisions with the dielectric boundary of the sample. The magnetic flux is included in the expression for the quasiparticle spectrum. The proximity effect and its influence on the spectrum of quantum coherent phenomena is investigated. The behavior of cylindrical samples consisting of a superconducting (S) metal with a deposited thin pure normal (N) metal layer is analyzed. In these structures, electrons are localized in a well bounded by a dielectric on one side and by a superconductor on the other. The resulting quantized Andreev levels have the feature that in a varying field H (or temperature T) each of the levels in the well can coincide periodically with the chemical potential of the metal. As a result, the state of the system has a strong degeneracy and the density of states exhibits resonance spikes as a function of the energy of the NS sample. This makes a significant contribution to the magnetic moment. A theory of the reentrant effect for NS structures has been developed for interpreting the anomalous behavior of the magnetic susceptibility of these structures as a function of magnetic field and temperature.