Einstein relationship and relaxation current in a tail at vanishing temperature -: art. no. 094203

We have applied our effective-medium method to an investigation of relaxation currents in tails. Our method yields explicit expressions for the calculation of the spectral transport coefficients, an Einstein relationship connecting them, and constituent equations governing the frequency dependence. The Einstein relationship shows that the sign of the relaxation current depends on the form of the density of states. Positive, zero, and negative relaxation currents are obtained, if the density of states increases, remains constant or decreases with increasing energy. Furthermore, we have applied our results to a discussion of the relaxation current in an exponential density of states within quasi-elastic approximation.