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Abstract:

Dynamic transport properties in various atomic devices were numerically investigated using the NEGF+DFT technique. For Al-C_n-Al structures, the real part and imaginary part of ac conductance oscillate versus the even-odd number of carbon atoms. Specifically, the dynamic part of ac conductance depends only on the parity of carbon atoms from low frequency up to THz. For all the carbon wires, although the transmission coefficients T are larger than 1/2, these systems show capacitive-like behaviors because the averaged transmission coefficients T_av are much smaller than 1/2. For an atomic nanocapacitor, the charge relaxation resistance is confirmed equal to half of resistance quantum h/2e² if there is only one transmission channel dominating the charge transport. An approximate method to calculate the time-dependent transient current by step-like pulse was proposed beyond the wide-band limit. Due to resonant states below the Fermi level, decay time of an atomic structure by an upward pulse can be very long. Each resonant state contributes a damped oscillation of transient current with oscillation frequency determined by the voltage and decay time determined by the width of the resonant peak. Numerical results demonstrated the necessity of going beyond the wide-band limit to obtain an accurate result of dynamic response in atomic devices.