Chemistry Reference
In-Depth Information
1
a
b
0.6
0.7
0.8
0.9
1.0
x=0.84
60
pump
0.8
C=
40
x=1
40
0.6
20
0.4
0
20
0
1
0.2
E
i
// chain axis
0
0
c
d
t
d
=0.16 ps
x
ph
=0.05
x
ph
=0.02
x
ph
=0.005
0.2
x
ph
=0.05
x
ph
=0.02
x
ph
=0.005
20
0.1
0
0
-20
e
f
t
d
=1.7 ps
x
ph
=0.05
x
ph
=0.02
x
ph
=0.005
x
ph
=0.05
x
ph
=0.02
x
ph
=0.005
0.2
20
0.1
0
0
-20
0
1
2
0
1
2
Photon energy (eV)
Photon energy (eV)
Fig. 5.15 (a, b) Polarized reflectivity (
R
) and
e
2
spectra along the chain (
solid lines
)in
[Pt(chxn)
2
I]I
2
.
Thin broken lines
in (b) show the
e
2
spectra of the MH state for various
C
values.
The
thick broken line
shows the
e
2
spectrum for the photoinduced metallic state (see text). The
inset in (b) shows the
e
2
spectra of [Ni
1
x
Pd
x
(chxn)
2
Br]Br
2
.(c)-(f) Photoinduced changes in
R
(
D
R
) and
e
2
(
D
e
2
) for three excitation densities at
t
d
¼
0.16 and 1.7 ps
increases at ca. 0.6 eV. Such spectral changes are very similar to those observed in
the CDW-MH transition of the PdBr-chain compound, which is discussed in
Sect.
5.4.1
. This indicates that the similar transition occurs in the PtI-chain com-
pound. For
x
ph
¼
e
2
has a large spectral weight below 0.2 eV,
suggesting a formation of a metallic state. At
t
d
¼
0.05 ph/Pt,
1.7 ps (Fig.
5.15f
), the spectral
shape of
e
2
is equal to that for
x
ph
¼
0.005 and 0.02 ph/Pt at
t
d
¼
0.16 ps. This
indicates that the metallic state quickly returns to the MH state.
Here we evaluate the conversion efficiency
f
of the CDW to MH transition. In
Fig.
5.16
, the magnitude of
D
e
2
(0.6 eV), characterizing the amount of
the MH state is plotted by solid circles for three
x
ph
values. The excitation density
dependence of
D
e
2
at 0.6 eV,
D
R
at 0.54 eV,
D
R
(0.54 eV), is also shown by open circles, which
coincides with that of
D
e
2
(0.6 eV). Therefore, we use
D
R
(0.54 eV) as a measure for
the amount of the MH state.
D
R
(0.54 eV) is proportional to
x
ph
for the low excitation
density (the broken line in Fig.
5.16
). It starts to deviate from the linear relation at
x
ph
~ 0.006 ph/Pt and tends to saturate for
x
ph
>
0.015 ph/Pt. Such saturation is
attributable to the space filling of the photogenerated species [
7
,
38
,
71
]. Assuming
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