K. Miyano and N. Takubo RCAST, U. of Tokyo Bidirectional optical phase control between a...
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![Page 1: K. Miyano and N. Takubo RCAST, U. of Tokyo Bidirectional optical phase control between a charge-ordered insulator and a metal in manganite thin films What.](https://reader036.fdocuments.net/reader036/viewer/2022062408/56649ee75503460f94bf80a9/html5/thumbnails/1.jpg)
K. Miyano and N. TakuboRCAST, U. of Tokyo
Bidirectional optical phase control between a charge-ordered insulator and a
metal in manganite thin films
What is it?motivationhistory of photoinduced transitionsample developmentresultsfuture
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What is optical bidirectional phase control?
manganite thin film
photoexcitation
COOI: charge- and orbital-ordered insulating stateFMM: ferromagnetic metallic state
COOI ’FMM’COOI ’ ……
pulse CW pulse ……
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motivation
to understand ‘colossal’ response in strongly-correlated electron systems => “inhomogeneity” is the keyword*
in particular, the effect of photoexcitation => ‘high energy’ excitation, far from equilibrium, instantaneous, high density, time-resolved spectroscopy …etc. => a ‘novel phase’ not accessible with ‘low energy’ stimuli e.g., T, H, E, …
* E.Dagotto, New J. Phys. 7, 67 (2005)
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history1: material
60 80 100 120 140 160 180 200 220 240 260 280 30010-2
10-1
100
101
102
103
104
105
106
107
0.50
0.40
0.30
0.20
0.10
Pr1-x
CaxMnO
3 resistivity
x = 0.10 x = 0.20 x = 0.30 x = 0.40 x = 0.50
resi
stiv
ity (
cm)
temperature (K)
Tomioka et al. PRB53, R1689 (1996)
P: paramagneticF: ferromagneticAF: antiferromagneticI: insulator
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2: discovery
1
102
104
106
108
0 1 2 3 4
↓
Pr0.7 Ca0.3 MnO3
Laser pulse (5 ns)
100μTime ( s)
Res
ista
nce
(Ω)
Tomioka et al. J.Phys.Soc.Jpn. 64, 3626 (1995)
‘colossal effect’
AF COOI => FMM
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3: problems
not persistent = conducting state remains only while current is kept => phase transition?needs potential across electrodes at photoinduced transition => driven by current or photoexcitation?
but WHY?
local transition = IMT is 1st-order with lattice distortion => stress from the surrounding COOI undo the transition? => make it small or thin
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4: ‘film’ is not good enough
0 500 10001500200025003000
0.75
0.80
0.85
0.90
0.95
1.00
65nm
260nm
Laser offLaser onLaser off
R/R
0
Time (sec)
Pr0.5Ca0.5Mn0.96Cr0.04O3/MgO(001)
20K, 633nm, 1mW/cm2
7m
photoinduced persistent conductivityMFM observation80K
film thickness
H. Oshima, M. Nakamura, and K. Miyano, Phys. Rev. B63, 075111 (2001).
H. Oshima et al.,PRB 63, 075111 and 094420 (2001).
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sample development need a thin film with a clear 1st-order phase transition (IMT) i.e., forgive large lattice distortion
=> use (110) substrates
(001)
tetragonal symmetryconserved
(110)
shear deformationallowed
Y. Ogimoto et al., Phys. Rev. B 71, 060403(R) (2005)Y. Ogimoto et al., Appl. Phys. Lett. 86, 112513 (2005)M. Nakamura et al., Appl. Phys. Lett. 86, 182504 (2005).
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tetragonal distortion predetermines the orbital = electronic states
Z. Fang et al. PRL (2000)
x=0.5
on (001) substrates:
C-type AFM FM A-type AFM
< ca ~ b ~ c > c
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clear transition
magnetictransportstructural
Nd0.5Sr0.5MnO3
Pr0.5Sr0.5MnO3
a: in-planeb,c: tilted
Wakabayashi et al., cond-mat/0506544
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bicritical point
Chaikin and Lubensky“Principles of condensed matter physics”
Y.Tomioka and Y.Tokura,Phys.Rev.B 66,104416(2002)
Pr1-x(Ca1-ySry)xMnO3 (Single Crystals)
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bicritical point in thin film
0 50 100 150 200 250 30010- 3
10- 2
10- 1
100
101
102
103
104
Resi
stiv
ity
(Ωcm
)
Temperature (K)
y=0.20
y=0.25
y=0.30 y=0.40
COO
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phase diagrams
Pr0.55(Ca1-ySry)0.45MnO3
Y.Tomioka and Y.Tokura,Phys.Rev.B 66,104416(2002)
bulk vs. thin films
TC
TCO
0 50 100 150 200 250 30010- 4
10- 3
10- 2
10- 1
100
101
102
103
104
Resi
stiv
ity
(Ωcm
)
Temperature (K)
(y=0.25)
5 T
3 T
1 T
0 T
2 T
4 T
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photoinduced phase transition (to lower T phase)
YAG OPO Pulse Laser
λ=637 nm 0.5 mJ/pulse rep rate 10 Hz
(y=0.25)
0 50 100 150 200 250 300 350102
103
104
105
106
107
108
109
Resi
stan
ce (
Ω)
Time (Sec)
Laser (100 pulses)
T=77 K
50 100 150 200 250 300103
104
105
106
107
108
109
Resi
stan
ce (
Ω)
Temperature (K)
Laser
0 50 100 150 200 250 30010- 2
10- 1
100
101
102
103
ρ(Ω
cm
)
T(K)
stable, persistent, no assisting field
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photoinduced phase transition: shot by shot
single shotone shot is not enough
multiple shots
· each shot is stable· effect of shots arecumulative
I (mJ/cm2)
R(
)1.95 eV
threshold
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photoinduced phase transition: dynamics
need to destroy charge gap= triggered by collapse of COO
nucleation and growth<= pumping rate percolation
essential physics
transition heating
all-optical write-erase memory
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futureclear case of 1st-order phase transition involving charge + spin + lattice
parameters: U + V + t (s, + J + g + T + H +
study:nucleation and growthscalingtime-resolved (pump and probe)dynamics electronic magnetic
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summary
establish film growth technique => clear COOI to FMM transitionseparate electronic excitation from heating => bidirectional phase control“soft and complex matter in solid form” => looks and feels hard but deformablecolossal response vs inhomogeneity => understanding strongly-correlated electron systems? (optical measurement is a way to go)
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collaborators
Naoko TakuboYusuke UozuHiroharu TamaruMakoto Izumi
Yoshinori TokuraYasuhide TomiokaHideki KuwaharaYoichi Murakami
current work force Yasushi OgimotoManfred FiebigTakao MoriToru TonogaiMikhail Milyaev
visitors in the past
Many students in the pastother institutions