  Time-dependent nonequilibrium Green's functions are used to study electron
transport properties in a device consisting of two linear chain leads and a
time-dependent interleads coupling that is switched on non-adiabatically. We
derive a numerically exact expression for the particle current and examine its
characteristics as it evolves in time from the transient regime to the
long-time steady-state regime. We find that just after switch-on the current
initially overshoots the expected long-time steady-state value, oscillates and
decays as a power law, and eventually settles to a steady-state value
consistent with the value calculated using the Landauer formula. The power-law
parameters depend on the values of the applied bias voltage, the strength of
the couplings, and the speed of the switch-on. In particular, the oscillating
transient current decays away longer for lower bias voltages. Furthermore, the
power-law decay nature of the current suggests an equivalent series
resistor-inductor-capacitor circuit wherein all of the components have
time-dependent properties. Such dynamical resistive, inductive, and capacitive
influences are generic in nano-circuites where dynamical switches are
incorporated. We also examine the characteristics of the dynamical current in a
nano-oscillator modeled by introducing a sinusoidally modulated interleads
coupling between the two leads. We find that the current does not strictly
follow the sinusoidal form of the coupling. In particular, the maximum current
does not occur during times when the leads are exactly aligned. Instead, the
times when the maximum current occurs depend on the values of the bias
potential, nearest-neighbor coupling, and the interleads coupling.
