Photoinduced nano and micron structures

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Photoinduced nano and micron structures
h?
K. Nasu
Solid state theory division, Institute of
materials structure science, High energy
accelerator research organization (KEK)
Graduate university for advanced study,
Tsukuba, Japan
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Photoinduced nano and micron structures
There discovered a new class of insulating
solids, which, being shined by only a few visible
photons, become pregnant with an excited nano or
micron domain, that has new structural and
electronic orders (, charge, spin, gauge ), quite
different from the starting ground state.


Purpose
Clarify, 1) conditions of its occurrence (,
hidden multi-stability ), 2) its mechanism (,
criticality, initial condition sensitivity ),
3) difference from thermally excited nano
domain, and finally establish the way how
to control nano domain.

K.Nasu et. al J.P.CM, 13 (2001) R693-R721.
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Excited
 
Hidden multistability
Lattice relaxation
Franck- Condon state
Excited nano domain
Photo-induced structural change
New latticestructureandelectronicorder
h?
Energy
h?
False ground state
Thermalenergy
Ground state
Microscopic
Order parameter of
lattice
Phase transition
distortion
Proliferation
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Neutral-ionic phase transition in TTF-CA

• Tc84K

Neutral (D0A0) ? Ionic(DA-)
Charge Transfer ?
0.3 ? 0.8

• DDimerization

Monomer phase
Neutral Phase (D0A0) P121/n1
Ionic Phase (DA-) P1n1
A-
D0
A0
A-
A0
D
D
D0
A0
D0
A-
D
A-
D0
A0
A-
A0
Molecules at z0
Molecules at z0
Molecules at z0
Molecules at z0
Molecules at z1/2
Molecules at z1/2
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Difference between photoinduced phase and
thermally induced phase
Organo-metallic complex crystal
Paramagnetic phase Yello
( S 2 ), T gt 120K
Diamagnetic Phase Red ( S 0 ), T lt 120K
They are two equilibrium phases of this material.
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Yellow paramagnetic phase can also be generated
as a nonequilibrium phase by light,
even at low temperatures.
Red equilibrium diamagnetic phase (S0)
Yellow nonequilibriumparamagnetic phase (S2)
By S.Koshihara
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Low temperature photoinduced phase is
different from the thermal one
of high temperature.
Photoinduced phase can make a new broken symmetry
appear, even if it can never appear in any
equilibrium phases. Our knowledge on
materials based only on equilibrium phases is
insufficient.
Raman spectra
Thermal para-magnetic phase
300K
70K
Thermal dia- magnetic phase
Intensity ( arb. uinit )
Photoinduced paramagnetic phase
30K
250
750
1250
1750
T. Tayagaki and K. Tanaka, Phys.Rev.Letters.86
(2001)2886.
New parity violation only in photoinduced phase
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Lattice constant change in photoinduced phase
of metal complex
crystal Fe(ptz), X-ray structure analysis
High temperature paramagnetic phase
Photoinduced phase
Fe-N distance (A)
Low temperature diamagnetic phase
Spring-8, BL 2B2, by Y.
Moritomo, J.Phys.Soc.Jpn 71(202)2609.
Laser power
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It can never appear
as an equilibrium state.
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Nasu, Phys. Rev. B 67 (2003) 174111.
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Theory for real time dynamics of 1- and 2- D
many-exciton phonon systems
Franck-Condon states
Start with a large excess energy
Nonlinear proliferation Initial condition
sensitivity Fractal Pattern formation
Early stage
Tunneling
Photoinduced
stage
Ground
Nano domain
state
Lattice distortion (, total exciton number,
domain size )
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Many-exciton system in a reservoir
Quantum Transfer
Attraction, or Interaction
Proliferation
Non-
Large lattice
adiabaticity
relaxation
Master equation under Markov approximation
Bistability
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Time evolution after
single photon pulse excitation
Total Exciton Number
Total Energy/?
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Successive photon pulse excitation
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Time evolution of spatial pattern
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Isotropy and anisotropy of interexciton
interaction
anisotropic
isotropic
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Fractal pattern analysis
Perimeter area relation
Fractal dimension D
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Perimeter area relation
Anisotropic case
Case(3)
Nper
Case(2)
Anisotropic case is more efficient than isotropic
case.
Isotropic case
Ntotal
R.Yabuki, Phys. Letters, 2003.
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1D ? 2D crossover point
(1) -gt (2) -gt (3)
Anisotropy becomes strong.
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Interexciton interactions
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Mean field theory for frozen exciton
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Decay of frozen exciton