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Dynamics of Shuttle Devices

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1.4. THIS THESIS deposited in the gap between two gold electrodes. The gap, produced with break junction technique, has a width of 1 nm. The molecule (of diameter 0.7 nm) is bound to the electrodes due to van der Waals interaction. Around the equilibrium position the potential can be approximated by a harmonic po- tential and the molecule can be considered as attached by springs. We show a schematic representation of this idea in Fig. 1.2. In the experiment Park et al. sweep the voltage across the junction and register sudden increases in the current. The steps are separated by 5 meV. Since the lowest internal ex- citation energy of the C60 molecule is 35 meV one concludes that the slower center of mass motion could be involved in the process. This hypothesis is confirmed by the fact that the separation between the steps is independent of the charge on the C60 molecule and the theoretical estimate for the energy corresponding to the center of mass oscillation in the van der Waals potential is exactly 5 meV. The IV-curve measured in these experiments can be inter- preted in terms of shuttling [19], but also alternative explanations have been promoted [20, 21, 22]. Whether we are in presence of coherent or incoherent shuttling transport and to what extent the shuttling mechanism is involved in this set-up cannot be completely clarified by current measurement. The current-current correlation (also called current noise) was proposed by Fe- dorets et al. [19] for a better understanding of the underlying dynamics of the current jumps. For this reason the calculation of noise in shuttle devices has been performed by many different groups. We proposed a completely quantum formulation [23] that is also explained in detail in this thesis. 1.4 This thesis This thesis contains the description and analysis of the dynamics of two realizations of quantum shuttle devices. The models we consider describe both the mechanical and electrical degrees of freedom quantum mechanically. For the single dot quantum shuttle we extended an existing classical model proposed by Gorelik et al. [1]. For the triple dot case we adopted the model invented by Armour and MacKinnon [7]. In the following we outline the contents of the thesis: In Chapter 2 we introduce the two models called Single Dot Quantum Shuttle and Triple Dot Quantum Shuttle, the first being the quantum ex- tension also for the mechanical degree of freedom of the model originally proposed by Gorelik et al. [1] while the second is the model invented by Armour and MacKinnon [7]. Also in this model the oscillator is treated quantum mechanically and the central moving dot is flanked by two static dots. 15

Anteprima della Tesi di Andrea Donarini

Anteprima della tesi: Dynamics of Shuttle Devices, Pagina 5

Tesi di Dottorato

Dipartimento: Department if Micro and Nanotechnologies

Autore: Andrea Donarini Contatta »

Composta da 158 pagine.

 

Questa tesi ha raggiunto 319 click dal 01/02/2005.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.