Coulomb Drag at the Onset of Anderson Insulators

TL;DR

This paper investigates Coulomb drag in Anderson insulators, revealing distinct behaviors in Mott versus Efros-Shklovskii insulators, and proposes drag measurement as a tool to differentiate insulating states based on their electronic interactions.

Contribution

It demonstrates how Coulomb drag behavior differs between Mott and Efros-Shklovskii insulators and suggests using drag measurements to distinguish interacting from non-interacting insulating states.

Findings

In Mott insulators, trans-resistance increases with localization length.

In Efros-Shklovskii insulators, trans-resistance increases as localization length decreases.

Coulomb drag can serve as a diagnostic tool for insulating state interactions.

Abstract

It is shown that the Coulomb drag between two identical layers in the Anderson insulting state indicates a striking difference between the Mott and Efros-Shklovskii (ES) insulators. In the former, the trans-resistance $\rho_t$ is monotonically increasing with the localization length $\xi$; in the latter, the presence of a Coulomb gap leads to an opposite result: $\rho_t$ is enhanced with a decreasing $\xi$, with the same exponential factor as the single layer resistivity. This distinction reflects the relatively pronounced role of excited density fluctuations in the ES state, implied by the enhancement in the rate of hopping processes at low frequencies. The magnitude of drag is estimated for typical experimental parameters in the different cases. It is concluded that a measurement of drag can be used to distinguish between interacting and non-interacting insulating state.