The effect of dephasing on electron transport through a benzene molecule is carefully examined using a phenomenological model introduced by Büttiker. Within a tight-binding framework all the calculations are performed based on the Green's function formalism. We investigate the influence of dephasing on transmission probability and current-voltage characteristics for three different configurations (ortho, meta and para) of the molecular system depending on the locations of two contacting leads. The presence of dephasing provides a significant change in the spectral properties of the molecule and exhibits several interesting patterns that have so far remain unexplored.
The question of the conditions under which 1D systems support extended electronic eigenstates is addressed in a very general context. Using real space renormalisation group arguments we discuss the precise criteria for determining the entire spertrum of extended eigenstates and the corresponding eigenfunctions in disordered as well as quasiperiodic systems. For purposes of illustration we calculate a few selected eigenvalues and the corresponding extended eigenfunctions for the quasiperiodic copper-mean chain. So far, for the infinite copper-mean chain, only a single energy has been numerically shown to support an extended eigenstate [ You et al. (1991)] : we show analytically that there is in fact an infinite number of extended eigenstates in this lattice which form fragmented minibands.
Electronic transport in a one-dimensional mesoscopic ring threaded by a magnetic flux is studied in presence of Rashba and Dresselhaus spin-orbit interactions. A completely analytical technique within a tight-binding formalism unveils the spin-split bands in presence of the spin-orbit interactions and leads to a method of determining the strength of the Dresselhaus interaction. In addition to this, the persistent currents for ordered and disordered rings have been investigated numerically. It is observed that, the presence of the spin-orbit interaction, in general, leads to an enhanced amplitude of the persistent current. Numerical results corroborate the respective analytical findings.
A new type of correlated disorder is shown to be responsible for the appearance of extended electronic states in one-dimensional aperiodic systems like the Thue-Morse lattice. Our analysis leads to an understanding of the underlying reason for the extended states in this system, for which only numerical evidence is available in the literature so far. The present work also sheds light on the restrictive conditions under which the extended states are supported by this lattice. PACS numbers: 71.25. -s, 61.44.+p, 64.60.Ak, 71.20.AdThe role of correlated disorder in producing extended electronic states in one-dimensional disordered systems has been extensively discussed in the literature by now [1 -3]. The basic reason for the appearance of extended states in such cases has been traced to the existence of a certain type of short range clustering effect among the atoms, first pointed out by Dunlap, Wu, and Phillips [1] in their study of a distribution of random dimers on a host lattice. It was shown that at a certain energy value the composite transfer matrix for a dimer offers identity contribution to the full transfer matrix, so that at this energy the full disordered lattice effectively behaves as an ordered chain. These correlations have later been shown to persist at all length scales in several quasiperiodic lattices such as the copper mean chain and the period doubling lattice [2], leading to whole hierarchies of extended states.Instances of one-dimensional lattices are, however, known which offer more intriguing possibilities.One such example is the well-known Thue-Morse aperiodic sequence, in which there is numerical evidence of extended states [4], although there is no short range dimer-type positional correlation in this lattice. As we shall see in this paper, another kind of clustering effect manifests itself in this lattice, which cannot be analyzed by the standard method known so far and developed in detail in Refs. [1] and [2]. We may mention in this connection the recent work of Lin and Goda [5] concerning a problem of hierarchical distribution of potentials on a lattice, where they also find an infinite number of extended electronic eigenstates, although there are no dimer-type correlations. The present work therefore provides yet another example of an aperiodic lattice where the standard picture of correlated disorder does not work.In a recent work on the Thue-Morse lattice, Ryu, Oh, and Lee [4] have provided numerical evidence of the existence of extended electronic eigenstates at certain specified energies, based on the study of the trace map for this lattice. It has been shown that a particular value of the trace remains unchanged under a renormalization group transformation.By using a detailed multifractal analysis they found that the energies associated with this trace value correspond to extended eigenstates. This work, however, does not provide any analytical guideline for discerning the extended character of these eigenfunctions, and the physical mechanism underlying the behavior of these eig...
We examine spin dependent transport in a quantum interferometer composed of magnetic atomic sites based on transfer matrix formalism. The interferometer, threaded by a magnetic flux φ, is symmetrically attached to two semi-infinite one-dimensional (1D) non-magnetic electrodes, namely, source and drain. A simple tight-binding model is used to describe the bridge system, and, here we address numerically the conductance-energy and current-voltage characteristics as functions of the interferometer-to-electrode coupling strength, magnetic flux and the orientation of local the magnetic moments associated with each atomic site. Quite interestingly it is observed that, for φ = φ0/2 (φ0 = ch/e, the elementary flux-quantum) a logical XOR gate like response is observed, depending on the orientation of the local magnetic moments associated with the magnetic atoms in the upper and lower arms of the interferometer, and it can be changed by an externally applied gate magnetic field. This aspect may be utilized in designing a spin based electronic logic gate.
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