Effects of the finite duration of quantum tunneling in laser-assisted scanning tunneling microscopy

Previous measurements of tunnel conductance in heterostructures and experiments with Josephson junctions suggest quantum tunneling has a definite duration. We use semiclassical methods to determine the effects of this delay on the tunneling current in a laser-assisted STM. A planar–planar STM model is used with the exact multiple image potential, and the energy distribution for a free-electron metal. It is necessary to average over the phase at barrier entry, and iteration with back propagated solutions is required to obtain the transmission coefficients for evenly spaced phases and specified energies at barrier entry. The simulations suggest that the dependence of the tunneling current on the wavelength of illumination can serve as a basis for determining the duration of barrier traversal. A power flux density of 1011 W/m2 would be required at several wavelengths from 1 to 10 μm. It is possible that thermal effects could be separated from the modeled phenomena by determining the time dependence of the tunneling current with a pulsed laser. © 1994 John Wiley & Sons, Inc.

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