Even denominator fractional quantum Hall effects in high quality bilayer graphene

I will discuss experiments probing the ground states of bilayer graphene in graphite- and hexagonal boron nitride encapsulated devices, focusing on even denominator filling factors within the eight-fold quasi-degenerate lowest Landau level. We observe robust fractional quantum Hall states at half filling whenever the ground state is fully polarized within the first excited Landau (N=1) orbital of conventional quantum Hall systems, and compressible composite fermi liquid states when the ground state is polarized within the N=0 orbital. Thermodynamic and thermal activation measurements show that the energy gap for incompressible 1/2 states are large, reaching several Kelvin, and numerical simulations taking into account details of the bilayer graphene band structure support a Pfaffian ground state. We use electric fields to drive an orbital polarization transition between N=0 and N=1 orbitals at half filling. Direct measurement of the valley polarizability shows the existence of an unexpected intermediate phase with a charge gap but gapless neutral excitations.