Quantum properties of atomic-size contacts and wires

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Experimental characterization of simple
single-molecule junctions
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In collaboration with ...
Kamerlingh Onnes Laboratory, Leiden University
Darko Djukic Yves Noat Roel Smit
Carlos Untiedt JvR

• Leiden Marc van Hemert
• IBM Yorktown Heights Norton Lang
• Technical University of Denmark Kristian
  Thygesen, Karsten Jacobsen.

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Mechanically Controllable Break Junction
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Mechanically Controllable Break Junction
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(No Transcript)
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Conductance histogram for Au
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Conductance curve for Pt
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Conductance histogram for Pt
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Conductance curve for Pt/H2
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Conductance histogram for Pt/H2
Bias voltage 140 mV
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Principle of point contact spectroscopy
G decreases for eV gt h?
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Point contact spectrum for Pt/H2
Modulation 1 mV, 7 kHz Recording time 10
s Temperature 4.2 K
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Isotope shift
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Conductance fluctuations 3 examples
Au
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Principle of conductance fluctuationsin
ballistic contacts
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RMS fluctuations measured for Au
Gold
Au
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Conductance fluctuations
T 0.97 (1)
Smit et al., Nature 419, 906 (2002)
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More frequencies and stretching dependence
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New local density calculations
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Vibration modes of a Pt H2 Pt bridge
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Vibration modes for Deuterium, PtD2Pt
PtD2
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Vibration modes for Deuterium, PtD2Pt
PtD2
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PtD2
K.S.Thygesen and K.W. Jacobsen (unpublished)
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Comparison H2 and D2
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Scaling of the modes by vm
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Scaling of the modes by vm
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A test case for model calculations
N. Lang (Nature 419 (2002) 906) .
Conduction by antibonding orbitals. G 0.9 G0.
M.C. van Hemert, (Nature 419 (2002) 906)
J. Kuipers and M.C. van Hemert, unpublished
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A test case for model calculations
Y. Garcia, J.J. Palacios, et al., cond-mat/0310098
Conduction by bonding orbitals. ?E23eV. G 0.2
G0.
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A test case for model calculations
J. Heurich, F. Pauli, J.C. Cuevas, W. Wenzel and
G. Schön, Nanotechnology 14 (2003) R29.
Conduction by bonding orbitals. ?E 24eV. G
0.86 G0
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A test case for model calculations
K. Thygesen and K.W. Jacobsen, unpublished.
Conduction by antibonding orbitals. ?E 10-13
eV. G 1.0 G0
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CO and Pt (preliminary)
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Conclusions

• Molecular hydrogen forms a nearly ideal conductor
  when placed between Pt electrodes, despite the
  closed-shell character of the free molecule.
• Single-molecule junctions can be characterized by
  the vibration modes, their stretching dependence,
  by the conductance and by the number of
  conduction channels.
• Hydrogen forms a good test-case for model
  calculations.
• More work on larger organic molecules

Universiteit Leiden
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Switching behavior for HD
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Switching during stretching
PtHD puzzle