1 / 49

Current Transfer, circular currents and magnetic field effects in molecular systems

Current Transfer, circular currents and magnetic field effects in molecular systems. With: Vered Ben Moshe, David Beratan , Oded Hod , Ron Naaman , Dhurba Rai , Spiros Skourtis , David Waldek. Beijing 2012. electron transfer. electron transmission. ELECTRON TRANSFER AND TRANSMISSION.

alagan
Download Presentation

Current Transfer, circular currents and magnetic field effects in molecular systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Current Transfer, circular currents and magnetic field effects in molecular systems With: Vered Ben Moshe, David Beratan, OdedHod, Ron Naaman, DhurbaRai, SpirosSkourtis, David Waldek Beijing 2012

  2. electron transfer electron transmission ELECTRON TRANSFER AND TRANSMISSION

  3. Current transfer • Circular Currents • Magnetic filed effects

  4. CURRENT TRANSFER • A charge transfer process in which the transferred charge carrier maintains at least some of its linear and/or angular momentum.

  5. D A D B NB A CURRENT TRANSFER

  6. J. Güdde, M. Rohleder, T. Meier, S. W. Koch, U. Höfer SCIENCE VOL 318 2007 Photoemission from the image potential state of Cu(100) excited with different parallel momenta (red dots – excess electrons)

  7. Science, 283, 814 (1999)

  8. J. J. Wei, C. Schafmeister, G. Bird, A. Paul, R. Naaman, and D. H. Waldeck J. Phys. Chem. B 110, 1301 (2006) NOTES: (a) The Porphyrin looses electron to acceptor in solution, then get it back from gold (b) Reversing molecular handedness has similar effect as reversing circular polarization (see statistics below)

  9. Current transfer in wires

  10. TIME DEPENDENT ANALYSIS PRL 101, 238103 (2008).

  11. Effect of decoherence

  12. STEADY STATE ANALYSIS

  13. Current asymmetry factor A2

  14. Circular currents

  15. Circular Currents

  16. circular currents and magnetic fields • Aharonov Bohm effect • Persistent currents (mesoscopic physics – Imry, Buttiker, Landauer) • NMR spectroscopy: Magnetic shielding effects (Pauling, London) • Excitation by shaped light pulses or circularly polarized light

  17. Ic I1 Itot Itot I2 Circular currents How to define the circular current?

  18. Magnetic Field Bio-Savart law: r – position vector of the point of observation r’ – position vector of the current element

  19. Definition: Ic is the only source of magnetic field in the ring (Oded Hod) I1 Itot R Itot I2 The component of the current which nulls the self induced magnetic flux threading the ring. The component of the current which nulls the magnetic field at the center of the ring. The component of the current which nulls the magnetic moment at the center of the ring.

  20. para meta ortho

  21. Transmission Coefficients Bond “transmission” coefficient Circular “transmission” coefficient

  22. [Meta-connected benzene] The transmission probability (full black line; left axis) and the circular transmission probability (dashed red line; right axis) as functions of the incoming electron energy E in the vicinity of the transmission resonance at 1eV. Variation of the circular current (left axis), and the magnetic field (right axis) at the center of the meta-connected benzene

  23. Naphthalene: V = 0 - 3 Volts V > 3 Volts 9/14

  24. Azulene: Electrodes in para position: No circular current. V = 0 to 2 Volts V > 2 Volts

  25. AharonovBohm Effect Oded Hod, PhD thesis TAU 2005 AB periodicity R=10-9 m R=10-6 m

  26. (a) conduction must be dominated by degenerate (in the free molecule) molecular electronic resonances, associated with multiple pathways as is often the case with ring molecules (b) molecular-leads electronic coupling must be weak so as to affect relatively distinct conduction resonances, (c) molecular binding to the leads must be asymmetric (e.g., for benzene, connection in the meta or ortho, but not para, configurations) (d) dephasing has to be small.

  27. Circular current as a function of bias voltage in the range (1.994 to 2.006 Volt) in a meta-connected benzene for in the presence of external magnetic field, B = 0, +/- 1T and +/- 5T. Molecule-lead coupling is 0.05eV. The inset depicts the case for molecule-lead coupling 0.5eV for applied field B = 0, +/- 100 T. For V≠0 I(B) ≠I(-B)

  28. para Transmission through para connected Benzene The transmission probability and I-V Characteristics of a junction comprising para- connected benzene coupled to the leads with coupling element 0.05 eV, evaluated for different magnetic field strengths B normal to the ring. In the main panel the results obtained for different magnetic fields for the para system are essentially indistinguishable from each other. The inset in this figure shows a close-up on the V = 2 V neighborhood that shows the consequence of the split degeneracy in the para-connected junction.

  29. Transmission through meta connected Benzene (a) Transmission probability around E=1eV through a junction comprising meta- connected benzene coupled to the leads with coupling matrix element 0.05 eV, evaluated for different magnetic field strengths B normal to the plane of the ring. (b) The current voltage behavior of this junction for the different magnetic field intensities. The inset in Fig. 2b shows the same current-voltage plots for molecule-leads coupling 0.5eV.

  30. g=1200 g=1800

  31. Effect of dephasing Transmission probability as a function of energy in the presence of dephasing: Top, and bottom figures correspond to para- and meta-connected benzene molecules, with molecule-leads coupling taken 1 eV. Left: Results obtained using the Büttiker probe model with the indicated coupling parameter . Right: results obtained by the density-matrix calculation with the indicated dephasing rate η.

  32. The integrated transmission for different dephasing strengths (imposed by the Buttiker probe method) near the molecular resonance at 1 eV (voltage bias 2V). Left – para connected benzene. Right - meta

  33. Magnetic field dependence of the current near the 2V step (associated with the transmission resonance at V=1V) calculated for a weakly coupled (βKM=0.05eV ) meta-connected junction with dephasing implemented by the Büttiker probe method (βBM=0.1eV). (b) and (c) The same magnetic field dependence expressed by the ratio [I(B)-I(0)]/I(0), plotted respectively against the dephasing parameters βBM (Büttiker probe method) and η (density matrix method). The inset in 17c displays the results of the main figure on a different scale, emphasizing the observation (also seen in 17a) of deviations from symmetry at intermediate dephasing rates.

  34. summary • Current transfer • Current transfer – a coherent process • Asymmetry factors • Decoherence effects • Steady state-dependence on boundary conditions • Circular currents - strong magnetic fields • Effects of external magnetic fields should be observable (meta connection, small dephasing)

  35. eF fL(E) – fR(E) T(E) eF T(E) fL(E) – fR(E) CONDUCTION I g Weber et al, Chem. Phys. 2002 F

More Related