Measurement of electronic transport through 1G₀ gold contacts under laser irradiation

Metal quantum point contacts (MQPCs) with dimensions comparable to the de Broglie wavelength of conducting electrons reveal ballistic transport of electrons and quantized conductance in units of G₀ = 2e ²/h. We measure the transport properties of 1G₀ Au contacts under laser irradiation. The observed enhancement of conductance appears to be wavelength-dependent, while thermal effects on conductance are determined to be negligible. For wavelengths that are not absorbed by Au, the results are consistent with a photoassisted transport mechanism in which conductance depends both on the electronic structure of the leads and on the interaction of the transporting electrons with oscillating electric fields originating from excitation of local plasmons. For wavelengths absorbed by Au, photoinduced mechanism is suggested to be the dominant transport mechanism. The results demonstrate optical control of ballistic transport in MQPCs and are also important for future interpretation of light effects on the conductance of single-molecule junctions.