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 84

Fig. 6.3 (a) Circuit for
current oscillation using an
NDR sample. (b) Currents I s
( dots ) and I b ( broken line ) are
plotted versus voltages V pq .
(c) Temporal profile of the
current with and without the
external capacitor. (d)
Temporal profile of the
voltage V pq with and without
the external capacitor.
Reprinted with permission
from [ 6 ]. Copyright (2009),
American Institute of Physics
combination of NDR materials and external circuits leads to the current and voltage
oscillation. The circuit is shown in Fig. 6.3a . By adding a serial resistor R s to the
NDR sample, we obtain the region in which the current increases with the increase
of the voltage, which is located above the NDR region, as shown by filled dots in
Fig. 6.3b . Resultantly, the current-voltage characteristic has an S-shape. Then, we
add a voltage source V b and a load resistor R L . The I - V curve between points p and
q through V b and R L is shown by a dotted line in Fig. 6.3b . The intersection of the
dotted line and the S-shape curve (dots) gives a stationary solution of this circuit
before attaching the capacitor. Moreover, by adding a parallel capacitor C ,we
obtain the nonstationary solution leading to the current oscillation. In Fig. 6.3c, d ,
we show the temporal profile of the current and voltage. In these figures, gray dots
indicate the waveforms before attaching the capacitor and filled dots are those after
attaching the capacitor. In the case of no capacitor (gray in Fig. 6.3c, d ), the current
increases along the lower branch of the S-shape curve and reach the stationary
point. Meanwhile, the voltage passes a larger value than the stationary point. On the