Spin and Charge Transport in Carbon-based Molecular Devices

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Spin and Charge Transport in Carbon-based
Molecular Devices

• Rafael Gutierrez
• Molecular Computing Group
• University of Regensburg
• Germany

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Carbon-based electronics

http//www.pa.msu.edu/cmp/csc/nanotube.html
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Outline
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Methodology
Green function techniques
F. Grossmann, RG and R. Schmidt, ChemPhysChem 3,
101 (2002)
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CNT-C60-CNT junctions
Motivation C. Joachim et al. Phys. Rev. B 58,
16407 (1998)  compression  J. J. Palacios
et al. Nanotechnology 12, 160 (2001) charge
transfer

doping
Alternative way to modify the transmission ?
RG, G. Fagas, G. Cuniberti, F. Grossmann, K.
Richter, and R. Schmidt, Phys. Rev. B65, 11341
(2002)
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• Structural optimization is essential
• Strong mixing of CNT-states with C60 molecular
  orbitals lifting of degeneracies

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• Strong orientational dependence of the
  conductance!
• Variations of 2-3 orders of magnitude near EF

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Do the caps introduce something new ?
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Evolution of the projected DOS with increasing
(a-gtd) CNT-C60 separation
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Metallisation via unconventional MIGS
NO !
RG, G. Fagas,K. Richter, F. Grossmann and R.
Schmidt, Europhys. Lett. 62, 90 (2003)
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Switching behaviour
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GMR in FM-MWCNT-FM junctions
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A minimal model
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Paramagnetic case P0

• Conductance(EF ,tin0) 2G0 for full contacted
  MWCNT expected value for infinite metallic DWCNT
  4G0 (tin0)
• channel blocking charge transferCNT-metal
  contact symmetry

see also e.g., S. Sanvito et al. Phys. Rev.
Lett. 84, 1974 (2000) J. J. Palacios et al.
Phys. Rev. Lett. 90, 106801 (2003)
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Ferromagnetic case P0.5

• full contact GMR lt 0
• partial contact GMR gt 0
• GMR weakly affected by tin
• Charge neutrality essential

S. Krompiewski, RG and G. Cuniberti,
cond-mat/0402359
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Elastic transport
charge
spin
CNT-C60-CNT
GMR in FM-DWCNT-FM junctions
(capped) CNT-C60-CNT
Incommensurability structural disorder
Inelastic transport electron-vibron
coupling Keldysh NEGF techniques

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Acknowledgements
G. Cuniberti (MC-Group,Uni Regensburg) G. Fagas
(NMRC, Cork, Ireland, Poster) K. Richter (Uni
Regensburg) S. Krompiewski (IfMP-Poznan,
Poster) M. Hartung (Uni Regensburg, Poster) N.
Ranjan (TU-Dresden, Poster) G. Seifert (TU
Dresden, Talk Fri. 1135) F. Grossmann
(TU-Dresden) R. Schmidt (TU-Dresden) A. Di Carlo
(Tor Vergata, Rome, Talk Wed. 1430) A. Pecchia
(Tor Vergata, Rome, Poster) M. Gheorghe (Uni
Regensburg, Poster) C. Böhme (Uni Marburg)
MPIPKSADMOL