Nonlinear Electrical Conductivity, Current Oscillation and Its Control in Halogen-Bridged Nickel(III) Compounds - Material Designs and New Physical Properties in MX-and MMX-Chain Compounds - page 88

the change in resistance [ 18 ]. In such studies, the reduction of the sample size leads
to the realization of fast oscillation up to 0.2 MHz [ 20 ]. In view of this, we may
realize faster oscillation in thin films of the present materials.
Moreover, the V b dependence of the current is shown in Fig. 6.5c . Experimen-
tally, the period decreases with increasing V b between 300 and 500 V. No oscilla-
tion is observed outside this range. This behavior is reproduced by the calculation
(Fig. 6.5d ). In the case of the lower and higher V b , the intersection of the load line
and the I - V curves falls on not negative resistance state but high- or low-resistance
state with a positive slope, respectively. In such cases, we do not obtain the
oscillation.
The dependence on R L is shown in Fig. 6.5e . The experimental data show the
increase of the period with increasing R L . This behavior can be roughly explained
by the calculation (Fig. 6.5f ). As in the case of the V b dependence, the oscillation
occurs only when the intersection falls on the negative differential region of the I - V
curve.
The studies about the current path and the nonlinear conducting domains are also
important. In another type of one-dimensional Mott insulator, K-TCNQ, it is
revealed that the nonlinear current flows throughout the crystal [ 14 ]. However, it
is often discussed that the nonlinear-conducting current flows in a filamentary
current path. The study on the spatial information about the nonlinear current will
be important to clarify the mechanism of nonlinear conductivity.
6.5 Conclusions
We introduced the nonlinear-conducting behaviors in halogen-bridged nickel(III)
compounds, [Ni(chxn) 2 Br]Br 2 and [Ni(chxn) 2 Cl]Cl 2 . These two compounds com-
monly show nonlinear-conducting behaviors. At low current density region, they
show ohmic (linear) response, while they show clear negative differential resistance
behaviors by increasing the current density. By attaching the external circuit
components, we achieved and controlled the current oscillation. The mechanism
is clearly explained by the nonlinear circuit theory. This indicates that halogen-
bridged nickel(III) compounds can be a candidates of nonlinear circuit components.
Acknowledgments The authors thank Mr. Takafumi Ito, Mr. Atsuya Ito, Prof. Shinya Takaishi,
and Prof. Masahiro Yamashita for collaboration.
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