Spin Mesoscopics
From: Xavier Blase [
]
Sent: 13 September 2002 09:05
To: 
Subject: Joint CECAM/Ψk workshop
Dear Walter Temmerman,
Please find below a workshop proposal that we submit to your consideration for
funding. We have submitted the proposal to CECAM as well ...
Yours Sincerely, Xavier Blase, Christophe Delerue, Kurt
Stokbro
***************** CECAM/Ψk WORKSHOP PROPOSAL **************
ELECTRONIC TRANSPORT IN MOLECULAR SYSTEMS
to be held in Lyon as a joint CECAM-Ψk workshop
*************
1- Organizers
*************
Xavier Blase
CNRS and Departement de Physique des Materiaux
43 Bd du 11 Novembre 1918 - 69622 Villeurbanne, France.
Phone: +(33)4.72.43.12.03
Fax: +(33)4.72.43.26.48
E-Mail:
Christophe Delerue
IEMN - Dept. ISEN
41 boulevard Vauban, 59046 Lille Cedex, France
Phone: +(33)-3 20 30 40 53
Fax: +(33)-3 20 30 40 51
E-Mail: 
Kurt Stokbro
Mikroelektronik Centret (MIC), Technical University of Denmark,
Building 345E, East DK-2800 Kgs. Lyngby, Denmark.
Phone: +(45)-4525 5762
Fax: +(45)-4588 7762
E-Mail: 
*********************
2- Scientific content
*********************
With the advancement of techniques for characterizing and manipulating individual
nano-objects such as molecules, metallic nanowires or nanocrystals, there has
been significant progress in the development of nano-electronics and molecular
electronics in recent years. Several research groups have reported measurements
of electrical transport through single or small groups of molecules. Experimental
current-voltage I(V) curves display complex features which arise from the quantum
states of the system and from the large perturbation induced by the motion of
a single electron into the nanostructure. One critical issue is the interpretation
of the experiments which most of the time requires detailed calculations of
the transport properties. Predicting the electrical properties of nanostructures
theoretically is a very complex problem. Typically, for a molecule between two
electrodes, there are many processes involved in the transport: charge transfer
between the molecules and the electrodes, interaction of the levels with the
continuum states of the electrodes, strong electron-electron interactions, molecular
vibrations which may induce inelastic scattering. Another fundamental issue
is that the molecular devices are out of equilibrium whereas most of the state-of-the-art
electronic structure calculations are presently made for systems at equilibrium.
Up to now, computational techniques used to solve these problems have been based
on non-selfconsistent H\"uckel or tight-binding calculations [1-9] which
have provided valuable insights into the identification of the conduction mechanisms.
Recent works have dealt with first-principles calculations based on the density
functional theory, solving the problems self-consistently, which is crucial
to determine the level positions with accuracy [11-21]. However, many important
questions remain to be solved, such as those concerning the importance of exchange-
correlation effects [6,22] and electron-phonon couplings [23-26]. On the computational
side, many evelopments are still necessary, in particular to be able to study
the transport through molecules containing a large number of atoms, such as
oligomers, nanotubes, proteins or DNA. Relevance of the workshop
-------------------------
The developments above mentioned have resulted in the multiplication of sessions
or colloquia in international meetings. However, workshops on the computational
aspects of molecular electronic have been scarce. As emphasized below, a quantitative
description of molecular transport needs to integrate several complex effects
and it is difficult for a single person/group to gather expertise in all fields.
The organization of such a workshop and the discussions between experts in the
various aspects of transport should help in providing a large overview to all
participants and in defining the lines of work to be followed. Topics to be
discussed include non-exclusively:
a) Transport formalisms Various techniques have been used to calculate transport properties: scattering state formalisms [11-13], equilibrium or non-equilibrium [14-17] Green's function approaches, explicit integration in time of the Schr\"odinger equation [5,19-21], etc. Comparisons between all these different approaches are scarce in the literature and such a workshop should allow to better understand the connections and differences between available formalisms. Further, in terms of perspective, it is important to discuss the ability of these various techniques to be modified so as to incorporate self-consistency, electron-phonon and electron-electron interactions beyond semi-empirical or standard ab initio mean-field approximations. Finally, computer efficiency and the possibility of going towards order-N algorithms [5,18] are important issues to be discussed for a practical study of realistic systems.
b) Electron-electron correlations From standard Coulomb blockade effects in quantum dots to the Luttinger behavior reported in carbon nanotubes, electron-electron interactions can be crucial in reduced dimensionality systems. Beyond computer-efficient empirical tight-binding, extended Hückel or Hubbard model approaches, state-of-the-art ab initio calculations have been so far mainly performed at the DFT level. However, the DFT is a ground state formalism and quantities such as the band gap "offsets" at the contact of two conductors may be severely wrong. Further, the local density approximation is known to misbehave with localized states of the kind encountered in molecular systems. Better descriptions of the exchange-correlation interaction can be included in the Green's function formalisms via the common language of self-energy and attempts to go "beyond DFT" (using for example the GW approximation) have been recently explored [6,22].
c) Electron-phonon interactions In the case of 1D systems, Peierls distorsions and polaronic transport are well known phenomena where electron-phonon coupling is crucial. Electron-phonon coupling may be experimentally studied using STM spectroscopy of adsorbed molecules by taking the second derivative of the current versus appled voltage (Inelastic Electron Tunneling Spectroscopy) [23,24]. But the interpretation of the IETS spectra is matter of a lot of controversies. Further, critical problems to include the electron-phonon coupling are numerous. The complexity of the calculations rapidly increases with the number of vibrational modes involved in the process, and thus with the number of atoms in the molecules. For this reason, and beyond empirical models [8], calculations are presently limited to extremely small molecules (2-3 atoms) [25,26]. Another difficulty is the calculation of the non-equilibrium electronic populations on the molecules and on the leads in presence of inelastic tunneling, in particular taking into account the Pauli principle which must be verified in all the conduction channels. Strategies to include such effects in electronic transport formalisms will be discussed.
References:
-----------
[1] "Electronic transmission coefficient for the single-impurity problem
in the scattering-matrix approach", P. Sautet and C. Joachim, Phys. Rev.
B 38, 12238 (1988).
[2] "Molecule-interface coupling effects on electronic transport in molecular
wires", S.N. Yaliraki and M.A. Ratner, J. Chem. Phys. 109, 5036 (1998).
[3] "Theoretical study of electrical conduction through a molecule connected
to metallic nanocontacts", E.G. Emberly and G. Kirczenow, Phys. Rev. B
58, 10911 (1998).
[4] "Conductance spectra of molecular wires", W. Tian, S. Datta, S.
Hong, R. Reifenberger et al., J. Chem. Phys. 109, 2874 (1998).
[5] "Conduction mechanisms and magnetotransport in multiwalled carbon nanotubes",
S. Roche, F.Triozon, A. Rubio and D.Mayou, Phys. Rev. B 64, 121401(R) (2001).
[6] "Theory of electrical rectification in a molecular monolayer",
C. Krzeminski, C. Delerue, G. Allan, D. Vuillaume, and R.M. Metzger, Phys. Rev.
B 64, 085405 (2001).
[7] "Tight binding description of the electronic response of a molecular
device to an applied voltage", C. Krzeminski, C. Delerue, and G. Allan,
J. Phys. Chem. B 105, 6321 (2001).
[8] "Quantum Inelastic Conductance through Molecular Wires", H. Ness
and A.J. Fisher, Phys. Rev. Lett. 83, 452 (1999); "Coherent electron-phonon
coupling and polaronlike transport in molecular wires", H. Ness, S.A. Shevlin,
and A. J. Fisher, Phys. Rev. B 63, 125422 (2001).
[9] "Electronic transport through carbon nanotubes: Effects of structural
deformation and tube chirality", A.Maiti, A.Svizhenko, M.P.Anantram, Phys.
Rev. Lett. 88, 126805 (2002).
[10] "Environment and structure influence in DNA conduction", Christophe
Adessi, S. Walch, P.Anantram, Phys Rev. B (to appear).
[11] "Carbon-Atom Wires: Charge-Transfer Doping, Voltage Drop, and the
Effect of Distortions", N. D. Lang and Ph. Avouris , Phys. Rev. Lett. 84,
358 (2000).
[12] "First-principles study of electron transport through monatomic Al
and Na wires", N. Kobayashi, M. Brandbyge, M. Tuskada, Phys. Rev. B 62,
8430 (2000).
[13] "Transport in nanoscale conductors from first principles", M.
Di Ventra and N.D. Lang, Phys. Rev. B 65, 045402 (2001).
[14] "Ab initio modeling of quantum transport properties of molecular electronic
devices", J. Taylor, H. Guo, J. Wang, Phys. Rev. B 63, 245407 (2001).
[15] "Unified description of molecular conduction: From molecules to metallic
wires", P.S. Damle, A.W. Ghosh, and S. Datta, Phys. Rev. B 64, 201403 (2001).
[16] "Conductance, I-V curves, and negative differential resistance of
carbon atomic wires", B. Larade, J. Taylor, H. Mehrez, and H. Guo, Phys.
Rev. B 64, 075420 (2001).
[17] "Density-functional method for nonequilibrium electron transport",
M. Brandbyge, J.-L. Mozos, P.Ordej\'on, J.Taylor, K. Stokbro, Phys.Rev.B 65,
165401 (2002).
[18] "O(N) real-space method for ab initio quantum transport calculations:
application to carbon nanotube-metal contact", M. Buongiorno Nardelli,
J.-L. Fattebert, J. Bernholc, Phys. Rev. B 64, 245423 (2001).
[19] "Time-dependent Simulation of Conduction through a Molecule",
J.K. Thomson, O.F. Sankey, Phys. Stat. Sol (b) 226, 115 (2001).
[20] "Dynamical simulation of field emission in nanostructures", S.
Han, M.H. Lee, J. Him, Phys. Rev. B 65, 085405 (2002).
[21] "Non-equilibrium transport dynamics approach to transport", Ralph
Gebauer and Roberto Car, Workshop on Recent Developments in Electronic Structure
Method (ES2002), Berkeley, California.
[22] "Quasiparticule theory on tunnelling currents: a study of C2H4 adsorbed
on Si(001)", G.-M. Rignanese, X.Blase, S.G.louie, Phys. Rev. Lett. 87,
206405 (2001).
[23] "Oxidation of a Single Carbon Monoxide Molecule Manipulated and Induced
with a Scanning Tunneling Microscope", J. R. Hahn and W. Ho, Phys. rev.
Lett. 87, 166102 (2001).
[24] "Vibrational spectroscopy of CO/Cu(211) with a CO terminated tip",
F. Moresco, G. Meyer, K.H. Rieder, Mod. Phys. Lett. B 13, 709 (1999).
[25] "Theory of Single Molecule Vibrational Spectroscopy and Microscopy",
N. Lorente and M. Person, Phys. Rev. Lett. 85, 2997 (2000).
[26] "Symmetry Selection Rules for Vibrationally Inelastic Tunneling",
N. Lorente, M. Persson, L.J. Lauhon, W. Ho, Phys. Rev. Lett. 86, 2593 (2001).
******************************
3-4) Tentative list of speakers
*******************************
The workshop will be composed of six sessions (mornings and afternoons). The
last afternoon will be devoted to a round table and concluding comments. With
4 to 5 talks in each session (45 mns presentations including 15 mns discussion),
this should allow for 20 to 30 speakers to participate. We plan on opening the
workshop by an overview of recent experimental results, including a critical
discussion of the difficulties encountered and of the reliability of measurements.
Another session should be opened by a review of the physics of mesoscopic systems
in general (localization, scaling laws, Luttinger liquids, etc). Most invited
speakers listed below are experts in simulations/code development. G. Meyer
is an experimentalist and Gilles Montambaux an expert on the physics of mesoscopic
systems.
"*" = confirmed
By alphabetical order:
* Christophe Adessi, Center for Nanotechnology, NASA Ames Research Center, on
leave for Lyon, France.
* X. Blase, Department of Material Science and CNRS, France.
- Wanda Andreoni, IBM Zurich Research, Switzerland.
- Mads Brandbyge, Mikroelektronik Centret (MIC), Technical University of Denmark,
Denmark.
- J. Cornil, Center for Research on Molecular Electronics and Photonics, Belgium.
- Christophe Delerue, IEMN - Dept. ISEN, France.
- Ralph Gebauer, Princeton University, on leave for Trieste, Italy.
- Eberhard Gross,Freie Universitat Berlin, Germany.
- A.J. Fisher,University College, UK.
- Per Hyldgaard, Chalmers University of Technology, Sweden.
- Karsten Jacobsen, CAMP-DTU, Denmark.
- Christian Joachim, CEMES, France.
- A. Martin-Rodero, Universidad Autonoma de Madrid, Spain.
- G. Meyer, IBM Zurich, Switzerland.
- Rosa Di Felice and Elisa Molinari, INFM Center for Nanostructures, Italy.
- Gilles Montambaux, LPS-Orsay, France.
- Herv\'e Ness, DSM-CEA, France.
- Mats Persson, Chalmers University of Technology and Göteborg University,
Sweden.
* Stefan Roche, DRFMC/SPSMS-CEA, France.
* Kurt Stokbro, Mikroelektronik Centret (MIC), Technical University of Denmark,
Denmark.
- H. Tang, CEMES, France.
- Tchavdar N. Todorov, School of Mathematics and Physics, Queen's University
of Belfast, UK.
Overseas speakers
-----------------
- J. Bernholc, NCSU, USA.
- Supriyo Datta, Purdue University, USA.
- M. Di Ventra, Georgia Tech, USA.
- Hong Guo, McGill University, Canada.
- George Kirczenow, Simon Fraser University, Canada.
- N.D. Lang, IBM Research Division, USA.
- Mark A. Ratner, Northwestern University, Illinois, USA.
***********
5- Tutorial
***********
As emphasized above, transport in molecular systems is at the crossroads of
several fields and most invited speakers do not currently work on all above
mentioned aspects. As such, it will be asked to all participants to pay attention
to devote an important part of there contribution to presenting the physical
problems and methodology before showing results of simulations on specific systems.
Further, we plan on inviting an experimentalist and an expert in mesoscopic
systems for a better presentation of the field. If CECAM money is available
to support invited speakers, we are certainly very willing to devote a significant
portion of Ψk funding to allow young Ph-D or postdoctoral researchers interested
in the field of molecular conduction to attend the workshop and participate
to the discussions.
*********
6- Budget
*********
We have followed CECAM rules (see below) to estimate the budget. For this
three days workshop, we ask for 6000 Euros to be supported by the Ψk.
*****************
7- Co-sponsorship
*****************
The same workshop proposal has been submitted to CECAM. The same amount (6000
Euros) has been asked.
******************
8- Location/Timimg
******************
As it is intended to be a joint CECAM/Ψk workshop, we plan on organizing
it in Lyon. It should be a "standard" 3-days workshop to be held beginning
of June 2003.