Electrostatically induced quantum point contact in bilayer graphene

We report the fabrication of electrostatically defined nanostructures in encapsulated bilayer graphene, with leakage resistances below depletion gates as high as $R\sim 10$G$\mathrm{\Omega }$. This exceeds previously reported values of $R =~$10-100k$\Omega$.\cite{Zou2010,Yan2010,Zhu2016a} We attribute this improvement to the use of a graphite back gate. We realize two split gate devices which define an electronic channel on the scale of the Fermi-wavelength. A channel gate covering the gap between the split gates varies the charge carrier density in the channel. We observe device-dependent conductance quantization of $\mathrm{\Delta }G=2e^2\mathrm{/}h$ and $\mathrm{\Delta }G=4e^2\mathrm{/}h$. In quantizing magnetic fields normal to the sample plane, we recover the four- fold Landau level degeneracy of bilayer graphene. Unexpected mode crossings appear at the crossover between zero magnetic field and the quantum Hall regime.