As with any other quantum particle, an electron exhibits wavelike and particlelike characteristics. Which aspect predominates in a solid depends on how an electron interacts with its neighbors. According to the Bloch theorem, for instance, an electron placed in a periodic lattice behaves like an extended plane wave. However, when the number of free electrons in a solid becomes comparable to the number of the constituent atoms and the mutual electron-electron interaction becomes strong, electrons may lose their mobility.
The dual nature is most apparent in correlated-electron systems, such as the transition-metal oxides in which electron interactions strongly determine electronic properties. In the transition-metal ions, for example, d electrons experience competing forces: Coulombic repulsion tends to localize individual electrons at atomic lattice sites, while hybridization with the oxygen p electron states tends to delocalize the electrons. The subtle balance makes many of the transition-metal oxides excellent resources for studying and...
