We study the dynamics of the electron current in nanodevices where there aretime-varying components and interactions. These devices are a nanojunctionattached to heat baths and with dynamical electron-phonon interactions and ananojunction with photon beams incident and reflected at the channel. We usethe two-time nonequilibrium Green's functions technique to calculate thetime-dependent electron current flowing across the devices. We find thatwhenever a sudden change occurs in the device, the current takes time to reactto the abrupt change, overshoots, oscillates, and eventually settles down to asteady value. With dynamical electron-phonon interactions, the interactiongives rise to a net resistance that reduces the flow of current across thedevice when a source-drain bias potential is attached. In the presence ofdynamical electron-photon interactions, the photons drive the electrons toflow. The direction of flow, however, depends on the frequencies of theincident photons. Furthermore, the direction of electron flow in one lead isexactly opposite to the direction of flow in the other lead thereby resultingin no net change in current flowing across the device.
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