Quantum effects in the transport properties of nanoelectronic three-terminal Y-junction devices

We report on a theoretical study of the electrical properties of three-terminal ballistic junction (TBJ) devices, consisting of three perfect leads and a ballistic coupling region, using a multiterminal scattering-matrix approach and the Landauer-Büttiker transport theory. The calculations have been performed for TBJ devices with different structure properties, at both high and low temperatures, as well as at both small and large applied bias voltages. The study is focused on the effects of quantum scattering, which is treated by exact numerical calculations. It is shown that when operated in the push-pull fashion, i.e., by applying finite voltages $V_l=V$ and $V_r=-V$ to the left and right branches, the TBJ devices exhibit strong nonlinearities in the output voltage $V_c$ calculated at the central branch. At high temperatures, the output voltage $V_c$ as a function of V shows the same nonlinear characteristics as observed in recent theoretical analyses and experimental measurements. These high-temperature electrical characteristics are found to be qualitatively insensitive to the structure details of the devices and reveal little effect of quantum scattering. At low temperatures, the output voltage $V_c$ shows fluctuations, and can assume either negative or positive values, depending on the chemical potential, at small bias regions. These behaviors are explained in terms of the fluctuations seen in the transmissions between the terminals, while the transmission fluctuations are shown to arise from strong scattering by quasibound states formed in the junction cavity region and are therefore signatures of quantum effects. Based on the quantum fluctuation nature of the device characteristics, a single multilogic device, constructed with a single TBJ, with switching of the logic functions by means of a gate, is proposed.