Organisers

• Thomas Frauenheim (University of Bremen, Germany)
• Abraham Nitzan (Tel Aviv University, Israel)
• Heiko Weber (University of Erlangen-Nürnberg, Germany)

Supports

University of Bremen

   CECAM

DFG Priority Program 1243 ``Quantum transport on the molecular scale´´

Description

Molecular Electronics is recognized as a key candidate to succeed the silicon based technology once we have arrived at the end of the semiconductor roadmap. The use of organic molecules in nanoscale nonlinear circuits offers many opportunities for new types of devices, which will differ in fabrication, functionality, and architecture. But even the fundamental question how elec-trical current flows across a single molecule is not satisfactorily understood. The common goal of this workshop to bring together experimental and computational groups to stimulate exchange and to develop a full physical picture of molecular-scale charge transport.

State of the art

On the computational side, the workshop will combine two major directions: Model-based approaches familiar from mesoscopic physics (quantum dots) and theoretical chemistry (intramolecular charge transfer) over the years have been adapted to the molecular electronics context. In particular, this implies that analytical approaches and solutions have been developed by explicitly considering molecular properties and by accessing new parameter regimes appropriate for molecules [1,2]. Complementary, first-principle-based atomistic approaches to quantum transport of complete molecular devices (including coupling to leads/substrates) have been developed to feed the model type calculations and to achieve a predictive power relevant to experiment [3]. The latter include Density-Functional-Theory methods with improved functionals and more advanced many-particle/quasiparticle as well as fully time-dependent methods for accurate calculations of energies, couplings, and conductances. While the molecule itself has to be treated as a strongly inhomogeneous many-body system, the coupling to the leads in-duces non-equilibrium conditions. On the experimental side, the field of single-molecule contacts has been successful in contacting individual molecules using various techniques like mechanically controlled break junctions, electromigrated break junctions, nanoparticle dimers, Scanning tunneling microscopes, and more. The parameters range from ultralow temperatures to room temperature, with experiments in vacuum, in solvent or in electrolyte. Each technique has advantages and limitations, and the overall picture is only accessible by careful comparison of the entity of available data. Simultaneously, the community has experienced that structure property relationships are very interesting on the qualitative level, but have difficulties in reproducing results due to the nearly unavoidable sample-to-sample fluctu-ations [4]. This is also a major handicap for delivering reliable data for the comparison with theoretical predictions. Techniques to master these problems have matured [5,6] and now noise, Kondo physics, molecular magnetism, molecular spin crossover and other effects become visible on the single-molecule level, which is a very desirable development for addressing improved quantitative understanding by computational studies.

Scientific Objectives

The goal of this workshop is to bring theoreticians from the two major branches of model approaches and atomistic simulations together, in order to discuss and define possible interconnections and regions of common interest. Topics of discussion will be

• Current status of theory vs. experimental results in molecular electronics


• The role of electron correlation


• Theory and experiment on novel phenomenology: noise, non-linear response, optical and thermal /thermoelectric effects


• Control and functionality of molecular junctions


• Redox molecular junctions


• Single molecule magnetism and spintronics

Several key lectures on contemporary measurements are scheduled in order to uncover remaining and new challenges for the theory of molecular con-duction. Participants from both the experimental and computational-theoretical side are therefore highly welcome.

References

[1] G. Cuniberti, G. Fagas, K. Richter, eds. Introducing Molecular Electronics Lecture Notes in Physics 680 (Springer, 2005).
[2] M. Galperin, M.A. Ratner and A. Nitzan, Molecular Transport Junctions: Vibrational Effects, J. Phys.: Condens. Matter 19, 103201 (2007).
[3] A. Pecchia and A. Di Carlo, Rep. Prog. Phys 67 (2004) 1497; A. Di Carlo, A. Pecchia, L. Latessa, T. Frauenheim, and G. Seifert, Tight-binding DFT for Molecular Electronics (gDFTB)�, in: Introducing Molecular Electronics, Springer Series: Lecture Notes in Physics vol. 680; eds. G. Cuniberti, G. Fa-gas, K. Richter, New York, (2005) Chapter 5.
[4] L. Venkataraman, J. E. Klare, C. Nuckolls, M. S. Hybertsen and M. L. Steigerwald, Dependence of single-molecule junction conductance on mo-lecular con-formation, Nature 442, 904-907 (2006).
[5] E. L�rtscher, H. B. Weber, H. Riel, Statistical Approach to Investigating Transport through Single Molecules, Phys. Rev. Lett. 176807 (2007).
[6] R. Ward, N. J. Halas, J. W. Ciszek, J. M. Tour, Y. Wu, P. Nordlander, and D. Natelson, Simultaneous measurements of electronic conduction and Ra-man response in molecular junctions, Nano Lett. 8, 919-924 (2008).