Non-local Andreev reflection under ac bias

We theoretically analyze non-local electron transport in multi-terminal normal-metal-superconductor-normal-metal (NSN) devices in the presence of an external ac voltage bias. Our analysis reveals a number of interesting effects, such as, e. g., photon-assisted violation of balance between crossed Andreev reflection (CAR) and elastic cotunneling (EC). We demonstrate that at sufficiently small (typically subgap) frequencies of an external ac signal and at low temperatures the non-local conductance of the NSN device turns negative implying that in this regime CAR contribution to the non-local current dominates over that of EC. Our predictions can be directly tested in future experiments. Copyright (C) EPLA, 2009