橋本佑介 A,B

三野弘文 A 、山室智文 A 、蒲原俊樹 A 、神原大蔵 A 、松末俊夫 B

Jigang WangC 、 Chanjuan SunC 、河野淳一郎 C 、嶽山正二郎 D

千葉大院自然 A 、千葉大工 B 、ライス大 ECEC 、東大物研 D

Y. HashimotoA,B

H. MinoA, T. YamamuroA, T. KamoharaA, D. KanbaraA, T. MatsusueB, J. WangC, C. SunC, J. KonoC, S. TakeyamaD

Graduate School of Science and Technology, Chiba Univ.A 、Department of Engineering, Chiba Univ.B, ECE Dept., Rice Univ.C 、 ISS

P, Univ. of TokyoD

13aXD-14

High excitation effects in dilute magnetic semiconductor CdMnTe

希薄磁性半導体 CdMnTe における強励起効果

Magnetic Polarons

Mn spin

Exciton spine　

h

Free Exciton Magnetic Polaron (FEMP)

Localization only by sp-d exchange interaction

A Golnic, et. al. J. Phys. C16, 6073 (1983)M. Umehara, Phys. Rev. B 68, 193202 (2003)

Photo-induced ferromagnetismvia the FEMP

Free exciton magnetic polaron (FEMP) in CdMnTe

High quality CdMnTe sample

with low Mn concentration

He-Ne laser76 MHz Ti:Sapphire laser

250 kHz OPA laser1 kHz OPA laser

Exciton density 1012 – 1020

[cm-3]

CW and Time-resolved Photoluminescence

Current work :

Alloy potential fluctuation : Small

x = 5 ~ 10% → FEMP energy : Large

S. Takeyama, J. of Crys. Growth, 184-185 (1998) 917-920

Mn Concentration [%]

Localiza

tion

en

erg

y

105

Alloy Potential fluctuation

Localization energy of Magnetic Polaron

Free Exciton Magnetic Polarons

FEMP Bipolaron

Ferromagnetic Phase Transition via Free Exciton Magnetic Polarons ?

Experimental Setup for PL measurements

Laser

CCDor

Streak camera

Spectro-meter

Sample 1.4 K

Bulk Cd1-xMnxTex = 5%

Cd1-yMgyTe

Cd0.95Mn0.05Te

GaAs

Lasers

Laser Exciton density [/cm3] rs Wavelength

He-Ne 2.2 x 1013 33 634 nm

Ti: Sapphire 2.8 x 1015 6.6 400 nm

250KHz OPA 8.6 x 1017 1 700 nm

1KHz OPA 2.2 x 1020 0.15 634 nm

1 kHz OPA250 kHz OPATi: SapphireHe-Ne

1013 1014 1015 1016 1017 1018 1019 10201012

1210 0.1100

nrs

Excitation intensity: 1mW, Focus size: 200m, O.D. 1

aB = 6.7 nm nMott = 7.9 x 1017 [cm-3]

Low Excitation Limit Exciton Density 1012 - 1014 [cm-3]

Absorption: 4.2 K, PL: 1.4KPL Light source： He-Ne 633nm

Absorption

PL

1.6801.6701.6601.650

FEMP

FX

BMP

BMP'

Pho

tolu

min

esce

nce

Absorption

Photon energy [eV]

Distinct PL line of the FEMP appear !! FEMP binding energy 1.8 meV

Ti: S

1

kHz O

PA

25

0 kH

z OPA

He-N

e

1013

1014

1015

1016

1017

1018

1019

1020

1012

BX

Photoluminescence Exciton Density 1015 – 1016 [cm-3]

Ti:S

1 kH

z OPA

25

0 kH

z OPA

He-N

e

1013

1014

1015

1016

1017

1018

1019

1020

1012

Excitation intensity normalized PLExciton density 1015, 1016[cm-3]

FEMP PL intensity: SaturateFX PL intensity: Increase

PL

inte

nsi

ty

1.6761.6721.668Photon energy [eV]

FX

FEMP

1015

1016

BX

1.681.671.66

Photon energy [eV]

400

300

200

100

0T

ime

[ps]

Time Resolved Photoluminescence Exciton Density 8.6 x 1017 cm-3

1020

Ti: S

1

kHz O

PA

25

0 kH

z OPA

He-N

e

1013

1014

1015

1016

1017

1018

1019

1012

AB1.674eV1.667eV

BXEHP

PL

inte

nsi

ty

1.701.681.661.64Photon energy [eV]

t = 40 - 140 ps

Time Resolved Photoluminescence

Exciton Density 8.6 x 1017 cm-3

A: 1.674 eV ~ 150 ps BiexcitonB: 1.667 eV < 30 ps ?

A

Inverse Boltzman

1020

Ti: S

1

kHz O

PA

25

0 kH

z OPA

He-N

e

1013

1014

1015

1016

1017

1018

1019

1012

4

6

1

2

4

6

10

2

4

6

100

PL

inte

nsi

ty

10008006004002000

Time Delay [ps]

A (1.6768 ~ 1.6723 eV) B (1.6611 ~ 1.6656 eV)

Many Body Effect of FEMPs

Coupled two FEMPs has been expected to be more stable than single FEMP

Bi-polaron Bi-exciton

PhotoluminescenceExciton Density > Mott Density

Ti: S

1

kHz O

PA

25

0 kH

z OPA

He-N

e

1013

1014

1015

1016

1017

1018

1019

1020

1012

Electron hole plasma I4.2

Biexciton I1.6

Ph

otol

um

ines

cen

ce

1.681.661.641.62

Photon energy [eV]

Biexciton

12 K

I2I

3.3I

EHP I = 5.6 × 1018 [cm-3]

Exciton Density Dependence of Origin of Photoluminescence

FEMPElectron hole

PlasmaBiexciton

Ti: S

1

kHz O

PA

25

0 kH

z OPA

He-N

e

1013

1014

1015

1016

1017

1018

1019

1020

1012

Summary

PL measurements Exciton density: 1012 – 1020 [cm-3]

FEMP Biexciton

Electron hole plasma

Future work

Spin Dynamics Under Strong Excitation

Free Exciton Magnetic Polaron

Hole mass:

0960

810

.m

m

.m

m

e

e

e

h

Electron mass:

meVN

meVN

880

220

0

0

Hole14.4Å

Electron

64Å

The number of Mn ionelectron: 481hole: ~5.5

Mn spin

Exciton Density Dependence

When the exciton density is above 1018 cm-3 FEMP may disappear

1.5

1.0

0.5

0.0

FE

MP

bin

din

g en

ergy

[m

eV]

0.1 1 10 100 1000Exciton density (× 10

16) [cm-3]

Ti: S

1

kHz O

PA

25

0 kH

z OPA

He-N

e

1013

1014

1015

1016

1017

1018

1019

1020

1012

Excitation intensity normalized FEMP PL int.FEMP binding energy

Nor

mar

ized

FE

MP

PL

In

t.

0.1 1 10 100Exciton density (× 10

16) [cm-3]

0

Spin Relaxation Dynamics

]cm[~n 316104

][104~ 317 cmn ]cm[~n 318101

1013

1014

1015

1016

1017

1018

1019

1020

1012

-4x10-3

0

4

T

/T

20100Time delay [ps]

10x10-3

86420

T

/T

20100Time delay [ps]

-8x10-3

-4

0

T

/T

20100Time delay [ps]

5K

Time Resolved Photoluminescence

1.6901.6851.6801.6751.6701.665

300

200

100

0

1.4K

Ti: S

1

kHz O

PA

25

0 kH

z OPA

He-N

e

1013

1014

1015

1016

1017

1018

1019

1020

1012

1.681.671.66Photon energy [eV]

400

300

200

100

0

Tim

e [p

s]

250 kHz OPA laser 76 MHz OPA laser

1.4K

Experimental Setup for PL measurements

chopper

Movablemirror

Sample 13 K1kHz OPA&CPA

He-Ne

PhotodiodeSpectro-meter

Lock-in Amplifier

Discussions

1.665

1.660

1.655

1.650

1.645

PL

pea

k p

osit

ion

[eV

]

151050

Exciton density ( x 1018

) [cm-3

]

100x10-15

80

60

40

20

0

PL

inte

nsi

ty

151050Exciton density ( x 10

18) [cm

-3]

0

Mott transition

EHP Exciton

Excitation Dependence of the PL　Intensity

Excited with Ti:Sapphire Laser

2

4

1

2

4

10

2N

orm

ariz

ed P

L in

tens

ity

60.1

2 3 4 5 61

Exciton density (× 1016

) [cm-3]

FEMP FX

I1.28

I1.04

I1.0

meVEE FEMPBX 1G

X

X2BX

FEMP

meV.EFEMP 82

Peak position [eV]

Binding Energy[meV]

Absorption 1.6748

Biexciton 1.6741 0.7

FEMP 1.6722 2.6

meV.meV.EBX 3383 Estimate by the EBX (4.1 meV) on CdSe

Purpose

G

X

FEMP

BXX2

21 n/BX

ps~FEMP 10