We investigate multi-terminal quantum transport through single monocyclic aromatic annulene molecules, and their derivatives, using the nonequilibrium Green function approach in the selfconsistent Hartree-Fock approximation. A new device concept, the Quantum Interference Effect Transistor (QuIET) is proposed, exploiting perfect destructive interference stemming from molecular symmetry, and controlling current flow by introducing decoherence and/or elastic scattering that break the symmetry. This approach overcomes the fundamental problems of power dissipation and environmental sensitivity that beset many nanoscale device proposals.PACS numbers: 85.65.+h, 31.15.Ne, 03.65.Yz From the vacuum tube to the modern CMOS transistor, devices which control the flow of electrical current by modulating an electron energy barrier are ubiquitous in electronics. In this paradigm, a minimum energy of k B T must be dissipated to switch the current "on" and "off," necessitating incredible power dissipation at device densities approaching the atomic limit [1]. A possible alternative is to control electron flow using quantum interference [2,3,4,5]. In mesoscopic devices, quantum interference is typically tuned via the Aharanov-Bohm effect [6]; however, in nanoscale conductors such as single molecules, this is impractical due to the enormous magnetic fields required to produce a phase shift of order one radian. Similarly, a device based on an electrostatic phase shift [3,4] would, in small molecules, require voltages incompatible with structural stability. We propose a solution exploiting perfect destructive interference stemming from molecular symmetry, and controlling quantum transport by introducing decoherence or scattering from a third lead.As daunting as the fundamental problem of the switching mechanism, is the practical problem of nanofabrication [1]. In this respect, single molecules have a distinct advantage over other types of nanostructures, in that large numbers of identical devices can be readily synthesized. Single-molecule devices with two leads have been fabricated by a number of techniques [7]. Our transistor requires a third terminal coupled locally to the molecule, capacitively or via tunneling (see Fig. 1). To date, only global gating of single-molecule devices has been achieved [7]; recently, however, there has been significant progress toward a locally coupled third terminal [8].This Letter reports the results of our recent theoretical investigations into the use of interference effects to create molecular transistors, leading to a new device concept, which we call the Quantum Interference Effect Transistor (QuIET). We demonstrate that for all monocyclic aromatic annulenes, particular two-terminal configurations exist in which destructive interference blocks current flow, and that transistor behavior can be achieved by supplying tunable decoherence or scattering at a third site. We also propose a realistic model for introducing scattering in a controllable way, using an alkene chain of arbitrary length (cf. ...

We give a detailed discussion of the quantum interference effect transistor (QuIET), a proposed device which exploits the interference between electron paths through aromatic molecules to modulate the current flow. In the off state, perfect destructive interference stemming from the molecular symmetry blocks the current, while in the on state, the current is allowed to flow by locally introducing either decoherence or elastic scattering. Details of a model calculation demonstrating the efficacy of the QuIET are presented, and various fabrication scenarios are proposed, including the possibility of using conducting polymers to connect the QuIET with multiple leads.

We investigate electrical conduction through individual oligopeptide molecules thiol-bonded between gold nanocontacts using ab initio and semi-empirical techniques. Our theory explains for the first time these molecules' experimentally observed current-voltage characteristics, including both the magnitude and rectification of the current, and uses no adjustable parameters. We identify the mechanism of the observed current rectification, and predict that it will result in negative differential resistance at moderate biases. Our findings open the way to the realization of protein-based nanoelectronic devices.

Immunoassays are commonly used for clinical diagnosis, although interferences have been well documented. The streptavidin-biotin interaction provides an efficient and convenient method to manipulate assay components and is currently used in several immunoassay platforms. To date, there has been no report in the literature of interference from endogenous anti-streptavidin antibodies; however, such antibodies would potentially affect multiple diagnostic platforms. We report results from a patient being treated for thyroid dysfunction who demonstrated a T-uptake result of less than 0.2 and a nonlinear thyroid stimulating hormone dilution that suggested an immunoassay interference. Protein-A sepharose pretreatment corrected the nonlinear dilution and revealed an interference trend of falsely decreased results, as measured by sandwich assay, and falsely elevated results, as measured by competitive assay. The results of streptavidin-agarose adsorption were comparable to adsorption with protein-A sepharose. To our knowledge, this is the first published description of an endogenous anti-streptavidin antibody interfering with clinical laboratory assays.

A new expression for the branching ratio for the decay via the E1 process in the normal-deformed band of superdeformed nuclei is given within a simple two-level model. Using this expression, the spreading or tunneling width gamma (downward arrow) for superdeformed decay can be expressed entirely in terms of experimentally known quantities. We show how to determine the tunneling matrix element V from the measured value of gamma (downward arrow) and a statistical model of the energy levels. The accuracy of the two-level approximation is verified by considering the effects of the other normal-deformed states.