Interaction-induced spatial correlations in a disordered glass

A consequence of the disorder and Coulomb interaction competition is the electron-glass phase observed in several Anderson insulators. The disorder in these systems, typically degenerate semiconductors, is stronger than the interaction, more so the higher is the carrier concentration N of the system. Here we report on a feature observed in the electron-glass phase of InxO with the lowest N yet studied. The feature, resolved as a broad peak in field-effect measurements, has not been recognized in previously studied Anderson insulators. Several empirical facts associated with the phenomenon are consistent with the conjecture that it reflects a correlated charge distribution. In particular, the feature may be turned on and off by gate-voltage maneuvering, suggesting the relevance of charge arrangements. It may also be suppressed by either temperature, non-Ohmic field, or exposure to infrared illumination. After being washed out, the feature reappears when the system is allowed to relax for sufficiently long time. A puzzling aspect that arises is the apparent absence of the phenomenon when the carrier concentration increases above a certain value. This is reminiscent of the glass-transition conundrum, except that the role of temperature in the latter is played by disorder. Analysis of these findings highlights several issues that challenge our understanding of the disorder-interaction interplay in Anderson insulators.