  Interface engineered ferroelectricity in van der Waals heterostructures is of
broad interest both fundamentally and technologically for the applications in
neuromorphic computing and so on. In particular, the moir\'e ferroelectricity
in graphene/hexagonal boron nitride (hBN) heterostructures driven by charge
ordering instead of traditional lattice displacement has drawn considerable
attention because of its fascinating properties and promising high-frequency
programmable electrical polarization switching. Yet, the underlying mechanism
of the electronic ferroelectricity is still under debate. On the other hand,
combining the interface engineered ferroelectricity and strong correlations in
moir\'e heterostructures could enable the realization of novel quantum states
such as ferroelectric superconductivity and multiferroicity. Here we study the
electronic transport properties of twisted double bilayer graphene (TDBLG),
aligned with one of the neighbouring hBN. We observe a strong gating hysteresis
and ferroelectric-like behaviour, as well as the electronic ratchet effect. We
find that the top gate is anomalously screened. On the contrary, the back gate
is anomalously doubly efficient in injecting charges into graphene, that is,
the effective back gate capacitance is two times larger than its geometry
capacitance. This unexpected gate-tunable capacitance causes a dramatic change
of electric fields between forward and backward scans. The asymmetric gating
behaviours and anomalous change in capacitance could be explained with a simple
model involved with a spontaneous electric polarization between top hBN and
graphene. Our work provides more insights into the mysterious ferroelectricity
in graphene/hBN moir\'e heterostructures and paves the way to the understanding
of the underlying mechanism.
