  Van der Waals (vdW) assembly of two-dimensional materials has been long
recognized as a powerful tool to create unique systems with properties that
cannot be found in natural compounds. However, among the variety of vdW
heterostructures and their various properties, only a few have revealed
metallic and ferroelectric behaviour signatures. Here we show ferroelectric
semimetal made of double-gated double-layer graphene separated by an atomically
thin crystal of hexagonal boron nitride, which demonstrating high room
temperature mobility of the order of 10 m$^2$V$^{-1}$s$^{-1}$ and exhibits
robust ambipolar switching in response to the external electric field. The
observed hysteresis is tunable, reversible and persists above room temperature.
Our fabrication method expands the family of ferroelectric vdW compounds and
offers a route for developing novel phase-changing devices.
