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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
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 ……
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)
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
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
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
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).
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).
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
clear transition
magnetictransportstructural
Nd0.5Sr0.5MnO3
Pr0.5Sr0.5MnO3
a: in-planeb,c: tilted
Wakabayashi et al., cond-mat/0506544
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)
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
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
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
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
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
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
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)
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
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