Chemistry Reference
In-Depth Information
5
1
a
b
E
i
//
b
axis
pump
σ
(x=1)
σ
(x=0.84)
4
3
0.5
2
293 K
R(x=1)
R(x=0.84)
1
0
0
c
d
σ
(
x=
0.84)
σ
(x=1)
R(x=0.84)
R(x=1)
2
0.1
1
2
×
10
3
0.1
0
0
-1
-0.1
e
f
x
ph
= 0.025
10
3
t
d
=0.
2
5
p
s
t
d
=0.25 ps
0.
0
5
5
p
s
5 ps
2
0
p
s
20
ps
500 ps
×
5
×
5
500 ps
0
1
2
0
0.5
1
1.5
Photon energy (eV)
Photon energy (eV)
Fig. 5.10 (a, b) Polarized reflectivity (
R
) and optical conductivity (
) spectra with
E
i
//
b
for
[Pd(chxn)
2
Br]Br
2
(
x ¼
1) (
solid line
) and [Ni
0.16
Pd
0.84
(chxn)
2
Br]Br
2
(
x ¼
0.84) (
dashed line
)at
room temperature. (c, d) Differential reflectivity (
D
R
) and optical conductivity (
D
s
) spectra
between [Ni
0.16
Pd
0.84
(chxn)
2
Br]Br
2
(
x ¼
0.84) and [Pd(chxn)
2
Br]Br
2
(
x ¼
1). (e, f) Photoinduced
reflectivity change (
D
R
) and optical conductivity change (
D
s
) in [Pd(chxn)
2
Br]Br
2
(
x ¼
1) at
various delay times (
t
d
) after photoexcitation (
dots
).
Solid lines
are guides to the eye. The pump
energy is 1.55 eV [indicated by an
arrow
in (a)]. The excitation density (
x
ph
) is 0.025 photon/Pd.
The polarizations of the pump and probe lights are parallel to
b
s
To evaluate the photoconversion efficiency, we calculated photoinduced change
(
D
s
) spectra by KKT analysis of the
R
+
D
R
spectra. As shown Fig.
5.10f
,
D
s
also
coincides well with the differential spectrum (i.e.,
D
s ¼ sðx ¼
0
:
84
Þsðx ¼
1
Þ
in
Fig.
5.10d
). The spectral shape of the photoinduced
spectrum appears to be
almost independent of
t
d
up to 500 ps. By comparing the integrated intensity of the
induced absorption in the photoinduced
D
s
D
s
(the gray area in Fig.
5.10f
) with that of
differential spectrum (the gray area of
sðx ¼
0
:
84
Þsðx ¼
1
Þ
in Fig.
5.10d
), a
efficiency (
) of the CDW to MH conversion was evaluated to be 55 % at
t
d
¼
0.25 ps for
x
ph
¼
0.025 ph./Pd. From these values it can be deduced that an
MH domain produced by one photon consists of 22 Pd sites. The high efficiency of
the CDW-MH conversion can be attributed to the near-degeneracy of the CDW and
MH states.
f
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