Measurement of linear-response Coulomb drag in insulating a- bilayer systems

We report observations of the Coulomb drag effect between insulating a- Si1−xNbx films. We find that a linear-response transresistivity ( ρ d ) can only be realized over a limited range of experimental parameters. We observe an anomalous decrease in the single layer resistance and transresistance at low temperatures ( T < 3 K ) due to an additional non-linear response coupling, which is in need of further investigation. In this manuscript, we focus on the behaviour at not too low temperatures ( 3 K < T < 15 K ) , where the intralayer transport is unperturbed by the bilayer geometry, and the temperature dependence of ρ d is qualitatively consistent with the layers being Efros–Shklovskii-type (as opposed to Mott-type) Anderson insulators. This is in agreement with past studies on the low energy transport in insulating a- Si1−xNbx. We show that functionally the temperature dependence in this regime is consistent with the layers having a 3-d density of states. Comparison to single-layer samples shows that the effective layer thickness is indeed increased in the bilayer geometry.