Electronic quantum transport through inhomogeneous quantum wires F. Khoeini a , A.A. Shokri b,c,Ã , H. Farman a a School of Physics, Iran University of Science and Technology (IUST), Narmak, 16846 Tehran, Iran b Department of Physics, Payame Noor University (PNU), Nejatollahi St.159995-7613 Tehran, Iran c Computational Physical Sciences Research Laboratory, Department of Nano-Science, Institute for Research in Fundamental Science (IPM), P. O. Box 19395-5531, Tehran, Iran article info Article history: Received 24 January 2009 Received in revised form 16 March 2009 Accepted 22 April 2009 Available online 5 May 2009 PACS: 72.15.Rn 73.23.Ad 73.40.Gk 72.80.Ng Keywords: Ballistic transport Tunneling Quantum localization Disorder quantum well abstract In this work, we study electronic quantum transport properties of a quasi-one-dimensional inhomogeneous quantum wire attached to semi-infinite clean metallic leads, taking into account the influence of hopping parameter. The calculations are based on the tight-binding model and transfer matrix method, which the electron transmission probability of the system is analytically calculated. We then concentrate on localization length and density of states (DOS) with additional diagonal disorder for various strengths of the hopping parameters. Our results show that the transmission decreases when the wire length increases, or the hopping parameter reduces. Furthermore, we investigate the concentration influence of disorder on the localization properties in quasi-one-dimensional systems. Also, we found that the localization length is almost independent of the wire size, while it increases with the higher hopping parameter. By controlling the relevant parameters, such as disorder concentration, wire length and hopping parameters, the system can be tuned to yield either localized or extended states. The application of the predicted results may be useful in designing nano-electronic devices. & 2009 Elsevier B.V. All rights reserved. 1. Introduction The study of electronic transport in solids is one of the most powerful tools to investigate the fundamental properties of materials in condensed matter physics. In recent years, the study of electronic transport through quantum dots (QDs), quantum wires (QWs), molecular wires, polymer wires, and nanotubes have been the major areas of research in mesoscopic and nanoscopic physics [1–7]. The size and shape of QDs and QWs can be precisely controlled in today’s technology. The quantum wires and quantum dots are the fundamental building blocks in nano-electronic devices. The electronic structure of one-dimensional conductors is, however, important as a testing ground for application of novel ideas, such as the quantum–mechanical many-body technique. One of these interesting candidates is TTF-TCNQ (tetrathiafulva- lene-tetracyanoquinodimethane), being the first organic charge transfer salt [8,9]. On the other hand, the electron localization properties of the quasi-one-dimensional disordered solids are of interest, both experimentally and theoretically. A simple approach to this problem is given by the Anderson model [10]. This model describes the generic behavior of the motion of an electron in a disordered solid. The energy of this electron, and also the disorder strength, can determine the localization or delocalization of the quantum states. This implies the existence of transitions between localized and metallic phases in disordered electronic systems. Numerically, this model has been applied to systems of all dimensions with particular interest in the scaling behavior of the localization length and the existence of a metal–insulator transition [11,12]. One of the basic tools in these investigations is the transfer matrices describing the evolution of the wave function as a function of the length of the system. From the transfer matrices method, the Lyapunov exponents, which provide the localization length, can be calculated. in such calculations, the tight-binding model Hamiltonian can be written as H ¼ X j e j jjihjjþ X j ðt j;jþ1 jjihj þ 1jþ t jþ1;j jj þ 1ihjjÞ, (1) where jji is a localized state at site j and t is the hopping parameter, which is restricted to nearest neighbors. The on-site energies e j can be randomly chosen according to some distribu- tion, for example, a uniform distribution or a Gaussian one. In the uniform distribution, e j are obtained in the interval ½W=2; W=2, where W is the difference of the on-site energies between the ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E 1386-9477/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2009.04.029 Ã Corresponding author at: Department of Physics, Payame Noor University (PNU), Nejatollahi Street, 159995-7613 Tehran, Iran. Tel.: +982122835061; fax: +98 2122835058. E-mail address: aashokri@nano.ipm.ac.ir (A.A. Shokri). Physica E 41 (2009) 1533–1538