Hysteresis phenomena in electron tunnelling, induced by surface plasmons

Abstract

A high spatial resolution surface plasmon near field scanning tunnelling microscope (STM) has been used to study the properties of localised surface plasmon oscillations (SPOs) in so-called hot spots on a gold surface, where the local electromagnetic field is extremely high. A CW semiconductor laser and a femtosecond Ti:Sa laser were used to excite the plasmons and the SPO-excited tunnel current was used as the detector. When scanning the STM from negative to positive bias and reversed, hysteresis in the tunnel signal was found, excluding (or rather minimising) the role of the presence of a potential Casimir effect in the process. It was found, however, that a multiple image charge-induced double well potential may explain our experimental findings. The stepwise behaviour of the area of the observed hysteresis loops is a new, additional indication of the non-classical properties of SPOs.