Photon-assisted shot noise in the mesoscopic system with a toroidal carbon nanotube coupled to normal-metal leads perturbed by ac fields

Abstract

We have investigated the shot noise of a system with a toroidal carbon nanotube (TCN) coupled to two metal leads with applied microwave fields. The tunneling current operator is derived by determining the electron operators in different parts of the system. The Landauer-B\"uttiker-like current operator is also obtained, from which we obtain the time-dependent current fluctuation correlations, and consequently the spectral density of shot noise. The photon-assisted shot noise exhibits interesting behaviors due to the special properties of the TCN and the transport behaviors of electrons in multichannel mesoscopic systems. The quantum steps of the shot noise with respect to the source-drain bias reflect the quantum nature of the TCN, as well as the applied microwave field. The saturated value of the shot noise is suppressed by the applied microwave fields, and the suppression is strongly associated with the structure of the TCN. The obtained shot noises are sub-Poissonian when the source-drain bias increases to a definite value, and super-Poissonian shot noise appears below this value.