The time-resolved conductivity of isolated GaAs nanowires is investigated by optical-pump terahertz-probe time-domain spectroscopy. The electronic response exhibits a pronounced surface plasmon mode that forms within 300 fs before decaying within 10 ps as a result of charge trapping at the nanowire surface. The mobility is extracted using the Drude model for a plasmon and found to be remarkably high, being roughly one-third of that typical for bulk GaAs at room temperature.
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