Time-dependent Landauer-Buttiker formula: Application to transient dynamics in graphene nanoribbons

Article

关键词: FIELD-EFFECT TRANSISTORS;    QUANTUM TRANSPORT;    CONDUCTANCE;    WIRES;    SYSTEMS;   

DOI  :  10.1103/PhysRevB.89.085131

来源: SCIE

【 摘 要 】

In this work, we develop a time-dependent extension of the Landauer-Buttiker approach to study transient dynamics in time-dependent quantum transport through molecular junctions. A key feature of the approach is that it provides a closed integral expression for the time dependence of the density matrix of the molecular junction after switch-on of a bias in the leads or a perturbation in the junction, which in turn can be evaluated without the necessity of propagating individual single-particle orbitals or Green's functions. This allows for the study of time-dependent transport in large molecular systems coupled to wide-band leads. As an application of the formalism, we study the transient dynamics of zigzag and armchair graphene nanoribbons of different symmetries. We find that the transient times can exceed several hundreds of femtoseconds while displaying a long-time oscillatory motion related to multiple reflections of the density wave in the nanoribbons at the ribbon-lead interface. This temporal profile has a shape that scales with the length of the ribbons and is modulated by fast oscillations described by intraribbon and ribbon-lead transitions. Especially in the armchair nanoribbons there exists a sequence of quasistationary states related to reflections at the edge state located at the ribbon-lead interface. In the case of zigzag nanoribbons, there is a predominant oscillation frequency associated with virtual transitions between the edge states and the Fermi levels of the electrode. We further study the local bond currents in the nanoribbons and find that the parity of the edges strongly affects the path of the electrons in the nanoribbons. We finally study the behavior of the transients for various added potential profiles in the nanoribbons.

【 授权许可】

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