  The recent discovery of transient negative capacitance has sparked an intense
debate on the role of homogeneous and inhomogeneous mechanisms in polarizations
switching. In this work, we report observation of transient negative
capacitance in improper ferroelectric h-YbFeO3 films in a resistor-capacitor
circuit, and a concaved shape of anomaly in the voltage wave form, in the early
and late stage of the polarizations switching respectively. Using a
phenomenological model, we show that the early-stage negative capacitance is
likely due to the inhomogeneous switching involving nucleation and domain wall
motion, while the anomaly at the late stage, which appears to be a reminiscent
negative capacitance is the manifestation of the thermodynamically unstable
part of the free-energy landscape in the homogeneous switching. The complex
free-energy landscape in hexagonal ferrites may be the key to cause the abrupt
change in polarization switching speed and the corresponding anomaly. These
results reconcile the two seemingly conflicting mechanisms in the polarization
switching and highlight their different roles at different stages. The unique
energy-landscape in hexagonal ferrites that reveals the dual switching
mechanism suggests the promising application potential in terms of negative
capacitance.
