It is shown that electron tunneling can be stimulated by electron-plasmon-virtual photon interactions. Negative differential resistance exhibiting a threshold voltage and current density is expected for metalbarrier-metal structures.

The detection characteristics of point-contact W-Ni diodes at 10 MHz, 9.5 GHz, and 28.3 THz are investigated as a function of diode resistance (contact pressure). The experimental results are compared with predictions from tunneling theory taking into account circuit parameters. Good agreement is obtained when the relaxation behavior of the metallic whisker antenna is considered at infrared wavelengths.

We show that correlation currents arising from the superposition of pairs of states on distinct sides of a potential barrier in metal-barrier-metal structures can result in inelastic tunneling through the emission of surface plasmons. Net gain of an externally excited plasmon field is possible.

It is shown that the coherent coupling of radiation into metal-barrier-metal structures by surface plasmons, which reduces to the usual antenna coupling at low frequencies, can be efficient up to a frequency at least as high as the plasma resonance.

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