Quantum Transport through a DNA Wire in a Dissipative Environment

Abstract

Electronic transport through DNA wires in the presence of a strong dissipative environment is investigated. We show that new bath-induced electronic states are formed within the bandgap. These states show up in the linear conductance spectrum as a temperature dependent background and lead to a crossover from tunneling to thermal activated behavior with increasing temperature. Depending on the strength of the electron-bath coupling, the conductance at the Fermi level can show a weak exponential or even an algebraic length dependence. Our results suggest a new environmentalinduced transport mechanism. This might be relevant for the understanding of molecular conduction experiments in liquid solution, like those recently performed on poly(GC) oligomers in a water buffer (B. Xu et al., Nano Lett. 4, 1105 (2004)).In the emerging field of molecular electronics, DNA oligomers have drawn in the last decade the attention of both experimentalists and theoreticians [1]. This has been mainly motivated by DNA exciting potential applications which include its use as a template in molecular devices or by exploiting its self-assembling and selfrecognition properties [2]. Alternatively, DNA strands might act as molecular wires either in periodic conformations as in poly(GC), or by doping with metal cations as is the case of M-DNA [3]. As a consequence, the identification of the relevant charge transport channels in DNA systems becomes a crucial issue. Transport experiments in DNA derivatives are however quite controversial [4,5]. DNA has been characterized as insulating [6], semiconducting [7] or metallic [8,9]. It becomes then apparent that sample preparation and experimental conditions are more critical than in transport experiments on other nanoscale systems. Meanwhile, a variety of factors that appreciably control charge propagation along the double helix have been theoretically identified: static [10] and dynamical [11] disorder related to random base pair sequences and structural fluctuations, respectively, as well as environmental effects associated with correlated fluctuations of counterions [12] or with the formation of localised states within the bandgap [4,13].Recently, Xu et al. [9] have carried out transport experiments on poly(GC) oligomers in aqueous solution. These experiments are remarkable for different reasons: (i) it was shown that transport characteristics of single molecules were probed, (ii) the molecules displayed ohmic-like behavior in the low-bias I-V characteristics and (iii) the linear conductance showed an algebraic dependence g ∼ N −1 on the number N of base pairs. This latter result suggests the dominance of incoherent charge transport processes. Complex band structure calculations [14] for dry poly(GC) oligomers predict, on the contrary, a rather strong exponential dependence of the conductance on the wire length, a typical result for coherent tunneling through band gaps. Hence,

Electrical Conductance in Biological Molecules

“…On the other hand, using a combination of molecular mechanics (for conformation ensemble generation) and quantum mechanics (for electronic structure calculation), Starikov et al [52] have shown that molecular motion and mismatches can actually increase the conductance under certain conditions and provide more coupled electronic states. In yet another work [53] , quantum-mechanical simulations on a simple DNA model in contact with a heat bath showed significant electronic structure modulation, which could be useful in describing observed Ohmic behaviour in short DNA wires using a tunnelling approach. More recently, a complete ab-initio study using the nonequilibrium Green's function approach, was carried out by Song, et al [54] , to study the effects of the correlated stretching/twisting of a (GC) dimer.…”

“…Usually, tight-binding Hamiltonians are employed to describe electronic structures of DNA duplexes -both explicitly (in the form of the "fishbone", "ladder" and similar models -see, for example, [51,53,58,60,[64][65][66][67][68][69][70][71][72] and the pertinent review articles [3,[73][74][75][76][77] ) and implicitly (within the framework of Marcus-type theories of charge transfer, for example, [55,[78][79][80][81] and the references therein). These works were successful in qualitatively (and sometimes even quantitatively) describing numerous experimental data (see, for example, [42,56,57,82,83] and the references therein) on transfer of injected single holes (or injected single electrons) through DNA duplexes.…”

Green Function Techniques in the Treatment of Quantum Transport at the Molecular Scale

“…Finally, transport in bio-molecules attracted more attention, in particular electrical conductance of DNA [286,287,288,289,290].…”

“…For equilibrium problems, unitary transformations combined with variational approaches can be used, in non-equilibrium only recently some attempts were made to deal with the problem. [139] In this section we will consider the case of a multi-level electronic system in interaction with a bosonic bath [288,289]. We will use unitary transformation techniques to deal with the problem, but will only focus on the low-bias transport, so that strong non-equilibrium effects can be disregarded.…”

DNA Double Helices for Single Molecule Electronics

“…We put forward new experimental setups to reveal the predicted effect and discuss possible applications of the DNA. In particular, we propose a design of the single molecule analog of the Esaki diode.Two approaches are widely used to describe the DNA: ab initio calculations [21][22][23][24][25][26][27][28] and model-based Hamiltonians [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. The former can provide a detailed description but is currently limited to relatively short molecules (typically of the order of 10 base pairs long).…”