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a

b

1.5

probe at 0.54 eV

probe at 0.69 eV

x
ph
= 0.005

1

x
ph
= 0.05

x
ph
= 0.02

0.5

x
ph
= 0.005

0

c

0

10

20

Delay time (ps)

d

0.08

t
d
=0.16 ps

100-cm
-1
osc.

0.06

0.04

100 cm
-1

x10

0.02

0

67 cm
-1

-0.02

0

0.5

1

1.5

0

1

2

3

4

5

Photon energy (eV)

Delay time (ps)

Fig. 5.17 (a) Time profiles of normalized

D
R
(0.69 eV) for

x
ph
¼
0.005. (c) Oscillatory components extracted from (b) and the fitting curve (
solid line
) which

is the sum of the two damped oscillators shown in the lower part. (d) Probe-energy dependence of

the 100-cm
1
oscillation amplitude (
open circles
) and
D
R
(
t
d
¼
0.16 ps) (
solid circles
) for

x
ph
¼
0.005 ph/Pt. The
broken line
is the first derivative of
D
R
(
t
d
¼
0.16 ps)

D
R
(0.54 eV). (b) Time profile of

Let us proceed to the discussion about the dynamics of the PIPT. In Fig.
5.17a
,

the time profiles of normalized

D
R
(0.54 eV) are presented. The signal instanta-

neously rises, indicating that the MH domain is formed within the temporal

resolution (180 fs). The decay time of the MH domain is ca. 20 ps. These features

are independent of
x
ph
. Subsequently to the initial rise, the coherent oscillations are

observed similarly to the case of the CDW to MH transition in [Pd(chxn

Þ
2
Br]Br
2
.

D
R
(0.69 eV) for
x
ph
¼

To scrutinize the oscillations, we selected

0.005 ph/Pt,

which is plotted in Fig.
5.17b
, and extracted the oscillatory component by

subtracting the background rise and decay from

D
R
, which is plotted in

Fig.
5.17c
. The oscillatory component can be reproduced well by the sum of the

two damped oscillators,

X

2

D
R
osc
¼

A
i
cos

ðo
i
t y
i
Þ

exp

ðt

=

t
i
Þ

(5.4)

i

as shown by the solid line. Here,

o
i
is the oscillation frequency,

t
i
is the decay time,

and

y
i
is the initial phase. In the fitting procedure, the response function of the

measurement system was taken into account as a Gaussian profile. The two

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