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Theory of the spin-polarized STMiffbluegel/vortrag_1… · PPT file · Web view · 2007-06-21The...
Transcript of Theory of the spin-polarized STMiffbluegel/vortrag_1… · PPT file · Web view · 2007-06-21The...
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Sinn für Drehungen im Nanokosmos
Stefan Blügel
IFF-I, Institut für Festkörperforschung
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www.fz-juelich.de/iff/e_th1Marilyn Monroe
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Encore Celebrity Images
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www.fz-juelich.de/iff/e_th1Marilyn Monroe
Andy Warhol
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www.fz-juelich.de/iff/e_th1Reminder : Chirality
An object that cannot be superimposed on its mirror image
mirror
Chiral objectsNonsuperimposablemirror images
mirror
Nonchiral objectssuperimposablemirror images
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www.fz-juelich.de/iff/e_th1Chirale Moleküle
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www.fz-juelich.de/iff/e_th1Chirale Moleküle
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Reminder : Parity violation
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Parity principle: Right and left handed versions of chiral objects or processes should exist with equal probability
• Electro-weak interaction SU(2)L
• Parity violation in terrestrial Biopolymers: DNA
Exceptions:
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Drehimpuls L = m (v x r)
t -t v -v L -L
Time-inversion symmetry (1)
Rechtsdrehung vorwärts Rechtsdrehung rückwärts
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L
r
v
t -t v -v L -L
t -t
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Time-inversion symmetry (2)
Rechtsdrehung rückwärtsLinksdrehung vorwärts
Der zeitumgekehrte Prozess lässt sich physikalisch realisieren!
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Spatial inversion (parity)
Der spiegelbildliche Prozess (hier ebenfalls die umgekehrte Drehung) ist ebenfalls physikalisch realisierbar.
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Inversion hier veranschaulicht an hand der ähnlichen Spiegelung
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www.fz-juelich.de/iff/e_th1Helizität des Lichts
Die Intensität des Lichts bestimmtdie Anzahl der Photonen, die wie Teilchen agieren
Lichtgeschwindigkeit
50% aller Photonenhaben Chiralität= -1
50% aller Photonenhaben Chiralität= +1
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Der Photoelektrische Effekt
Metalloberfläche
Die Intensität des Lichts bestimmtdie Anzahl der Elektronen
50% aller Elektronenhaben Chiralität=-1/2 50% aller Elektronenhaben Chiralität= +1/2
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Spiral Galaxies
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Parity Violation at Surfaces
time inversion
Tmirror reflection
R
time inversion
Tmirror reflection
R
time inversion
T
E =E(TR)
E =E(TR)
E ≠E(TR)
mirror reflection
R
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www.fz-juelich.de/iff/e_th1Homochiral Magnetic State
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Consequences of symmetry breaking
|L> |R>
FM/AFM
E(c)
c
For magnetic nanostructure it holds that:If chirality can be broken, spin-orbit interaction will break it!
After 25 years of surface magnetism, is this of relevance oris it smoke of theory?
o Does ferro- or antiferromagnetism exists at surfaces at all ?o For domain walls, chirality can be broken i.e. there should be only walls of one type
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www.fz-juelich.de/iff/e_th1Complete Picture
HeisenbergExchange
DzyaloshinskiiMoriya-Exchange
Magneto-CrystallineAnisotropy
Dipol-DipolAnisotropy
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www.fz-juelich.de/iff/e_th1Phase Diagramme
M. Heide, G. Bihlmayer and S. Blügel
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Model system: Monolayer Mn on W(110)
0.75 ML
+ 10
0 m
eV/A
tom
+ 10
0 m
eV/A
tom
± 0
meV
/Ato
m±
0 m
eV/A
tom
+ 70
meV
/Ato
m+
70 m
eV/A
tom
Magnetic Configuration: Pseudomorphic Growth:
M. Bode et al., Surf. Sci. 432, 8 (1999).
Cu-Atome
Vakuum
Mn-Atome
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www.fz-juelich.de/iff/e_th1Imaging Mn/W(110)
Non-magnetic W-TipNon-magnetic W-Tip
S. Heinze, M. Bode et al.,
Science 288, 1805 (2000).
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Quantum Mechanics of Electrons: Many-body problem
iron atom:
26 electron wave-function: Ψ(r1,...r26)
store only 10 values per coordinate: 1078 values
assume each value could be stored
in a single H atom: memory heavier than the milky way
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Density Functional Theory (DFT)
Total Energy:
Secular Equation:
Density:
Energy is functional of electron density n and external parameterssuch as lattice constants, atoms positions, magnetization direction…
CPU time proportional to N3:
Selfconsistency loop
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The Nobel Prize in Chemistry 1998
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"for his development of the density-functional theory"
"for his development of computational methods in quantum chemistry"
Walter Kohn John A. Pople
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Revolution in Computing Power:
cutting supercomputing in nanomagnetism
A. E. Brenner, Physics Today, October 1996
$1K
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Imaging the Magnetic Ground State of 1ML-Mn/W(110)Non-magnetic W-TipNon-magnetic W-Tip Magnetic Fe-TipMagnetic Fe-Tip
First experimental Proof of the 2D-AFM!First experimental Proof of the 2D-AFM!S.Heinze, M. Bode, A. Kubetzka, X. Nie, O. Pietsch, S.Blügel, Wiesendanger, Science 288 (2000)
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Revolution in Computing Power:
cutting supercomputing in nanomagnetism
A. E. Brenner, Physics Today, October 1996
$1K
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New Interaction discovered
Bode, Heide, von Bergmann, Ferriani, Heinze, Bihlmayer, Kubetzka, Pietzsch, Blügel, Wiesendanger,
cycloidal spiral
x
Nature 447, 190 (2007)
|L> |R>
FM/AFM
E(c)
c
JUMP
λ =8nm =40atoms
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www.fz-juelich.de/iff/e_th1Tool-driven revolutions
Dyson, F., Imagined Worlds, Harvard University Press, Cambridge, MA, 1997, pgs. 50-51.
New directions in science are launched by new tools more often than by new scientific concepts.
The effect of a concept-driven revolution is to explainold things in new ways. The effect of a tool-driven re-volution is to discover new things that have to be explained. We have been more successful in dis-covering new things than in explaining old ones.
The computer incidentially caused a revolution in physics itself, increasing the power of physical theories to interpret experiments and predict phenomena. Thecomputer and the algorithms are prime example of an intellectual tool.
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Vision: Simulation Triangle@FZJ
Research AreaSimulation
JSF GRS
IAS
NICGAUSS
PACE
DEISA
JARA-SIMJPSS
Th. Lippert & S.Blügel
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Institute for Advanced Simulation (IAS)
• Computational Biotechnology • Computational Biophysics• Computational Nanoscience• Quantum Computing• Computational Neuroscience• Computation Engineering
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22 Artikel in Science
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54 Artikel in Nature
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• Markus Heide• Gustav Bihlmayer
Collaboration: Paolo Ferriani Stefan Heinze Matthias Bode Kirsten von Bergmann Nacho Pascual Ph. Hofmann
Helmholtz Association of Research Centers (HGF)Deutsche Forschungsgemeinschaft (DFG)
Sponsers:
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www.fz-juelich.de/iff/e_th1Theory-1 Group at IFF