Charge Imbalance: Its Relaxation, Diffusion and Oscillation
Broadly speaking, one can distinguish three different levels of description which have made decisive contributions to our understanding of condensed matter. On the coarsest time and length scales phenomena may be described in terms of a limited number of variables. This leads to descriptions such as hydrodynamics for liquids (two-fluid hydrodynamics for superfluids), elasticity theory for solids, and the Landau-Ginzburg equations for superconductors. At the other extreme one has fully microscopic descriptions, which are able to take into account rapid spatial and temporal variations. The price one pays for the increase in generality is the increased complexity of the formalism, and a large increase in the number of degrees of freedom that must be considered. For example, distribution functions must be used, rather than simply the total density. At this microscopic level the theory of superconductors, the BCS theory, has been spectacularly successful in making possible the understanding of a vast range of phenomena. By comparison, microscopic theories have had relatively little impact on work on the helium liquids.
KeywordsBoltzmann Equation Collective Mode Collision Term Charge Imbalance Coherence Factor
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