Estudo de transporte não recíproco e funções lógicas em cadeias discretas acopladas não linearmente

Abstract

Systems which exhibit nonreciprocal transmission or that can be used as logic functions are of great interest for the development of essential devices to nanotechnology. In this work, we investigate the transmission properties for two kinds of coupled discrete nonlinear chains configurations. In the first structure, it was explored the diode-like behavior, while in the other, it was showed the performance of different logic gates. The two systems were described by a set of the discrete nonlinear Schrödinger equations within a tight-binding approach. We determine their respective transmission spectrum. The first system is a nonlinear dimer coupled to linear side chains. We investigate the influence of the saturation of the nonlinear response on the nonreciprocal transmission, which had not been well studied in the previous literature. Through the analysis of the transmission spectrum, we unveil that, in regions of bistable behavior (windows), the difference between transport from right to left and transport from left to right is greater. Moreover these windows widen and displace to regions where the incident amplitude is larger as saturation is considered. The calculation of rectifying factor showed that, in the second bistability window, the influence of the saturation parameter has distinct actions over short- and long-wavelength. In the first window, the rectifying action is not compromised by the saturation. So weak saturation can improve the efficiency of the nonreciprocal transmission. The second system is a Y-shaped structure, on which three linear chains are joined by a nonlinear site. This kind of structure has been studied in the context of DNA-based devices. We investigated the capability of our model system to perform logic gate operations based on the transmission of phase-shifted incoming waves. Using a digitalization scheme of the output signal based on amplitude modulation, we show that AND, OR and XOR logic gate can be achieved. The phase-shifting between the incoming waves is required for the OR logic gate to be realizable and strong nonlinearity favors the existence of logic gates in the regime of short wavevectors. The analysis of the contrast ratio shows that optimal operation of the AND and OR logic gates takes place when the nonlinear response is the predominant physical property distinguishing the coupling and regular sites. We concluded that Y-shaped structures can potentially perform distinct logic functions.