Ultrafast dynamics in multiferroics HoMnO3 revealed

by fs spectroscopy

Chih Wei Luo (羅志偉)

Outline

Introduction of femtosecond (fs) laser pulses

Ultrafast dynamics in multiferroics HoMnO3Summary I

High-Tc superconductor YBa2Cu3O7 nanodots

Summary II

What is the ultrashort pulse?

~10-6 s

~10-9 s

~10-12 s~10-15 s

Introduction of fs laser pulses

Timescales

1 minute10 fs light

pulse Age of universe

Time (seconds)

Computer clock cycle

Camera flash

Age of pyramids

One month

Human existence

10-15 10-12 10-9 10-6 10-3 100 103 106 109 1012 1015 1018

1 femtosecond 1 picosecond

a pulse : 1 minute ~ 1 minute : age of universe

Introduction of fs laser pulses

Which one is true?

1 / 1 min

1 / 0.5 min

1 / 1 sec

Idea from 石訓全

Introduction of fs laser pulses

Ultrafast camera!!

Introduction of fs laser pulses

The possibility for nuclear fusion!

Introduction of fs laser pulses

Short pulse = intense peak power100 mJ, 100 fs = 1 TW1018 W/cm2 @ φ = 10 μm (1010 V/cm)

Institute of Laser EngineeringOsaka University

LegendLegend

AmplifierAmplifier

MiraMira

SeedSeed

VerdiVerdiPumpPump

EvolutionEvolutionPumpPump

Short pulse, low energy

Long pulse, high energy

Short pulse, high energy

LegendLegend

AmplifierAmplifier

MiraMira

SeedSeed

VerdiVerdiPumpPump

VerdiVerdiPumpPump

EvolutionEvolutionPumpPump

EvolutionEvolutionEvolutionEvolutionPumpPump

Short pulse, low energy

Long pulse, high energy

Short pulse, high energy

The shorter pulse duration, the more papers!

1950 1960 1970 1980 1990 2000 201010-18

10-15

10-12

10-9

intra-cavity pulse compression

XUV excitation pulse

Colliding pulse mode-locking

Passive mode-locking

Active mode-locking

Puls

e du

ratio

n (s

ec.)

Year

First laser (Ruby)

1980 1983 1986 1989 1992 1995 1998 2001 2004 20070

500

1000

1500

2000

Femtosecond in Web of Science

No.

of P

ublic

atio

ns

Year

Prof. Ahmed Zewail

The 1999 Nobel Prize in Chemistry

Prof. Theodor W. Hänsch

The 2005 Nobel Prize in Physics

The evolution of pulse width

Introduction of fs laser pulses

Multiferroic

Ultrafast dynamics in HoMnO3

Ferromagnets (ferroelectrics) form a subset of magnetically (electrically) polarizablematerials such as paramagnets and antiferromagnets (paraelectrics and antiferroelectrics)

W. Eerenstein, N.D. Mathur, J.F. Scott, Nature 442, 759 (2006). 

Multiferroic ReMnO3

Ultrafast dynamics in HoMnO3

Hexagonal structure      v.s.      Orthorhombic structure

Seongsu Lee, et al Nature 451,805 (2008) S. Satpathy, et al PRL 76 ,960 (1996)

W. Prellier, et al, JPCM 17, 803 (2005) 

Hexagonal HoMnO3

Ultrafast dynamics in HoMnO3

TC= 875 K Pz= 5.6 μC cm‐2

TN= 76 K TSR= 33 K THo= 5 K

Coexistence between FE and AFM 

MnO5 bipyramids form a layered structure on a‐b plane. 

B. Lorenz, et al PRB 71 ,014438 (2005)

Magnetoelectric coupling effect on hexagonal HoMnO3

Ultrafast dynamics in HoMnO3

Dielectric constant Heat capacity Lattice constant

B. Lorenz, et al PRL 92 ,087204 (2004)

B. Lorenz, et al PRB 71 ,014438 (2005)

C. Dela Cruz, et al PRB 71 ,060407R (2005)

Optical properties of hexagonal HoMnO3

Ultrafast dynamics in HoMnO3

Transmittance and reflectance measurements were performed using a Fourier transform spectrometer in a frequency range from 10 to 45000 cm-1 (1.2 meV to 5.6 eV)

1.7 eV absorption peak comes from d→d transitions.

~0.15 eV blueshift as decreasing temperature.

Associate with the magnetic phase transition.

A. B. Souchkov, et al PRL 91 ,027203 (2003)

e1g

e2g

a1g

Optical properties of hexagonal HoMnO3

Ultrafast dynamics in HoMnO3

Woo Seok Choi, et al PRB 78 ,054440 (2008)

TN

Rare‐earth : Gd、Tb、Dy、Ho

Crystal structure and magnetic property

Ultrafast dynamics in HoMnO3

Out of plane : c‐axisIn plane : ab‐axis

10 20 30 40 50 60

HM

O(0

06)

HM

O(0

04)

Inte

nsity

(arb

. uni

ts)

2θ (degree)

HM

O(0

02)

TN= 76 K TSR= 33 K THo= 5 K

0 20 40 60 80 100

2.0x10-6

4.0x10-6

6.0x10-6

8.0x10-6

1.0x10-5

1.2x10-5

0 50 100 150 200 250 300

1/χ

(Oe/

emu)

Temperature (K)

Curie-Weiss Law

TSRχ

(em

u/O

e)

Temperature (K)

ZFC 100 OeH//c-axis

THo

Pump-probe and optical spectroscopy

Ultrafast dynamics in HoMnO3

700 720 740 760 780 800 820 840 860 880

Nor

mal

ize

Inte

ntsi

ty (a

rb. u

nits

)

Wavelength (nm)

740nm 755nm 770nm 785nm 800nm 815nm

Tunable photon energy from 1.52 to 1.69 eV

Temperature-dependent transient reflectivity change (ΔR/R)

Ultrafast dynamics in HoMnO3

0 20 40 60 80

T=60K

T=67K

T=71K

T=80K

T=100K

T=140K

T=180K

T=220K

T=290K

Δ

R/R

(arb

. uni

ts)

Delay Time (ps)

0 20 40 60 80

T=210K

T=170K

T=150K

T=140K

T=120K

T=100K

T=60K

T=250K

x3

ΔR

/R (a

rb. u

nits

)

Delay Time (ps)

x3

T=290K

0 20 40 60 80

T=250K

T=210K

T=190K

T=170K

T=130K

T=110K

T=95K

T=85K

ΔR

/R (a

rb. u

nits

)

Delay Time (ps)

T=290K

Wavelength : 800 nm Wavelength : 770 nm Wavelength : 740 nm

Oscillation component

Ultrafast dynamics in HoMnO3

0 10 20 30 40 50

800nm 740nm

ΔR

/R (a

rb. u

nits

)

Delay time (ps)

T=290K

Strain Pulse Model )sin2/( 22 θυλτ −≅ nsoundprobeosc

D. Lim, et al APL 83 ,4800 (2003)

LuMnO3

Ultrafast dynamics in HoMnO3Charge transfer from e2g to a1g by pump pulses

223 rzd

−

levels3Mn3 d+

)(),( 22 xyyxd

−

E

Pump energy :1.52 eVP

ump energy

Pum

p energy

T=290K

T=140K

Room temperature Low temperature

Woo Seok Choi, et al PRB 78 ,054440 (2008)Observed the blueshift of energy gap !

0 50 100 150 200 250 300

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

am

plitu

de o

f ΔR

/R

Temperature (K)

815nm

T0=140 K

Ultrafast dynamics in HoMnO3Charge transfer from e2g to a1g by pump pulses

Observed the blueshift of energy gap !

0 50 100 150 200 250 300

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

am

plitu

de o

f ΔR

/R

Temperature (K)

815nm 800nm

levels3Mn3 d+ Pump energy :1.55 eVRoom temperature Low temperature

223 rzd

−

)(),( 22 xyyxd

−

E

Pum

p energy

Pum

p energy

T=290K

T=140K

Ultrafast dynamics in HoMnO3Charge transfer from e2g to a1g by pump pulses

Observed the blueshift of energy gap !

0 50 100 150 200 250 300

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

am

plitu

de o

f ΔR

/R

Temperature (K)

815nm 800nm

T0=117 K

levels3Mn3 d+ Pump energy :1.55 eVRoom temperature Low temperature

223 rzd

−

)(),( 22 xyyxd

−

E

Pum

p energy

Pum

p energy

T=290K

T=117K

T=140K

Ultrafast dynamics in HoMnO3Charge transfer from e2g to a1g by pump pulses

0 50 100 150 200 250 300

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

am

plitu

de o

f ΔR

/R

Temperature (K)

815nm 800nm 785nm 770nm 755nm 740nmT0

levels3Mn3 d+ Pump energy :1.68 eVRoom temperature Low temperature

T=63K

Pum

p energy

223 rzd

−

EP

ump energy

T=290K

)(),( 22 xyyxd

−

40 60 80 100 120 140 160 1800.00

0.04

0.08

0.12

0.16

0.20

Temperature (K)

Slop

e

40 60 80 100 120 140 160 1801.481.501.521.541.561.581.601.621.641.661.681.701.72

Temperature (K)

AFM

Ener

gy g

ap E

dd (e

V)

0 20 40 60 80 100

2.0x10-6

4.0x10-6

6.0x10-6

8.0x10-6

1.0x10-5

1.2x10-5

0 50 100 150 200 250 300

1/χ

(Oe/

emu)

Temperature (K)

Curie-Weiss Law

TSR

χ (e

mu/

Oe)

Temperature (K)

ZFC 100 OeH//c-axis

THo

Ultrafast dynamics in HoMnO3Charge transfer from e2g to a1g by pump pulses

0 50 100 150 200 250 300

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

am

plitu

de o

f ΔR

/R

Temperature (K)

815nm 800nm 785nm 770nm 755nm 740nmT0

levels3Mn3 d+ Pump energy :1.68 eVRoom temperature Low temperature

40 60 80 100 120 140 160 1800.00

0.04

0.08

0.12

0.16

0.20

Temperature (K)

Slop

e

40 60 80 100 120 140 160 1801.481.501.521.541.561.581.601.621.641.661.681.701.72

Temperature (K)

AFM

Ener

gy g

ap E

dd (e

V)

T=63K

Pum

p energy

223 rzd

−

EP

ump energy

T=290K

)(),( 22 xyyxd

−T=63K

Pum

p energy

)(),( 22 xyyxd

−

Extra‐blueshift comes from long‐range AFM ordering!!

Ultrafast dynamics in HoMnO3Demagnetization dynamics

0 20 40 60 80

0 100 200 300 400 500 600

75K

180K

290K

ΔR

/R (a

rb. u

nits

)

Delay time (ps)

Te Tl Tsτm

T=75K

T=180K

Delay time (ps)

T=290K

τmτc75 K

60 90 120 150 180 210 240

1

2

3

4

5

6

7

τ m

Temperature (K)

800nm 785nm 770nm 755nm 740nm

Summary

The oscillation due to the strain pulse was clearly observed in ΔR/R by fs spectroscopy.

A distinct blueshift of the Mn3+ d-d optical transition comes from the appearance of AFM long-range ordering.

The demagnetization time (τm) in a few psscale and its recovering time (τc) in a few 100 ps scale were shown in the ΔR/R.

0 10 20 30 40 50

800nm 740nm

ΔR

/R (a

rb. u

nits

)

Delay time (ps)

T=290K

0 50 100 150 200 250 300

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

am

plitu

de o

f ΔR

/R

Temperature (K)

815nm 800nm 785nm 770nm 755nm 740nmT0

0 20 40 60 80

Te Tl Tsτm

T=75K

T=180K

Delay time (ps)

T=290K

τm 75 K

YBCO nanodotsSample reparation:

Vacuum Pumps

VacuumGauges

Excimer Laser

Lens

YP

Heater

Vacuum ChamberO2

(001) YBa2Cu3O7 (YBCO) / (100) LaAlO3

10 20 30 40 50 60 700

100

200

300

400

YBC

O(0

03)

YBC

O(0

06)

YBC

O(0

07)

LAO

(200

)

YBC

O(0

05)

YBC

O(0

04)

LAO

(100

)

YBC

O(0

02)

YBC

O(0

01)

inte

nsity

(a. u

.)

2θ (degrees)

XRD

SEM

50 100 150 200 2500

5

10

15

Res

ista

nce

(Ω)

Temperature (K)

Tc = 90.1 K

YBCO nanodotsExperimental setup: (spot size~110 μm)

fs Laser

光路徑光路徑

LaAlO3

YBCO19.6 cm

YBCO nanodotsResults – surface morphology

Fluence = 0 J/cm2

Fluence = 0.21 J/cm2

Fluence = 0.26 J/cm2 Fluence = 0.53 J/cm2

Fluence = 0.32 J/cm2

C. W. Luo, C. C. Lee, et al., Optics Express 16, 20610 (2008)

YBCO nanodotsResults – structure

Fluence = 0 J/cm2 Fluence = 0.21 J/cm2

Fluence = 0.26 J/cm2 Fluence = 0.32 J/cm2

Fluence = 0.53 J/cm2

XRD signals of YBCO thin films at various laser fluences.

YBCO nanodotsResults – superconductivity

Fluence = 0 J/cm2 Fluence = 0.21 J/cm2

Fluence = 0.26 J/cm2 Fluence = 0.32 J/cm2

Fluence = 0.53 J/cm2

YBCO nanodotsResults – composition

Fluence = 0 J/cm2 Fluence = 0.21 J/cm2

Fluence = 0.26 J/cm2 Fluence = 0.32 J/cm2

Fluence = 0.53 J/cm2

3000 K > 1897 K (Ba)

3700 K > 3345 K (Y)

EDS spectra show the composition of area 1 and area 2.

314-

1-3-6

m 101.14 KmJ 102.86 /

mJ 0.1

×=×==Δ

≈

VCCVWTW

Summary

The surface microstructure of YBCO thin films can be manipulated by properly controlling the fluence of the irradiating femtosecond laser.

A ripple pattern was clearly observed on the surface of one YBCO thin film.

The (001)-YBCO film turns into nanodot arraywith the superconductivity remains almost intact.

Serve as a new way of engineering the material surfaces into nanometer scale structures.B. K. Nayak, et al., Appl. Phys. A 90, 399 (2008)Formation of nano-textured conical microstructures in titanium metal surface

Students: H. C. Shih, C. C. Lee, H. I. Wang, W. T. Tang

Solid State Lab: K. H. Wu, J. Y. Juang, J.-Y. Lin, T. M. Uen

NSRRC: J. M. Chen, J. M. Lee

Acknowledgements

Thank you

for your attention!!