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