This chapter presents a survey of the dc conductivity in electron glasses within the linear response regime. A deep understanding of the processes responsible for conductivity in the steady state is necessary for attempting to treat the out-of equilibrium phenomena of the conductivity. Special emphasis is given to the effect of electron-electron interactions, which lead to the Coulomb gap and to correlated electronic transitions. These are essential for understanding the glassy properties in these materials.

Section 5.1 is devoted to review the main experimental results on dc conductivity, with emphasis on materials where glassy effects are observed. The different elements needed for conductivity theory in an electron glass are discussed in Section 5.2. The different types of hopping transport are described in Section 5.3, with emphasis on variable range hopping (VRH). The most frequently used approach to solve the previous model is percolation theory, which will be elaborated upon in Section 5.4. Scaling theory is the other approach employed to understand these problems and is reviewed in Section 5.5. The algorithms employed in numerical simulations are detailed in Section 5.6, together with their main results on conductivity. Finally, concluding remarks are summarized.

dc Conductivity: experimental

Impurity conduction in doped semiconductors

If one could pinpoint when serious interest began in understanding the microscopic physics of disordered systems, many would probably agree that observation of impurity conduction at low temperatures provided the driving incentive. These date back to the late 1940s in SiC (Busch and Labhart, 1946).