Localized plasmons in point contacts

Abstract

Using a hydrodynamic model of the electron fluid in a point contact geometry we show that localized plasmons are likely to exist near the constriction. We attempt to relate these plasmons to the recent experimental observation of deviations of the quantum point contact conductance from ideal integer quantization. As a function of temperature, this deviation exhibits an activated behaviour, , with a density-dependent activation temperature of the order of 2 K. We suggest that can be identified with the energy needed to excite localized plasmons, and we discuss the conductance deviations in terms of a simple theoretical model involving quasiparticle lifetime broadening due to coupling to the localized plasmons.