Speaker: Ali Yazdani (Princeton University) Title:Â A charged vortex lattice in an exciton superfluid Abstract:Â Lattices of quantized vortices are a defining property of rotating superfluids and of type-II superconductors in magnetic fields. Realizing an analogous vortex lattice in an exciton superfluid - formed from bound electron-hole pairs - has remained challenging because excitons are electrically neutral. Theory has predicted that in a strong magnetic field, a weakly charged exciton superfluid can stabilize a vortex-antivortex lattice arising from the mutual repulsion of fractionally charged vortex cores. I describe spatial resolved STM experiments on condensates forms between Landau levels of two graphene layers separated by a thin hexagonal boron nitride barrier in a perpendicular magnetic field. We find a charged lattice that has all the predicted properties of the predicted vortex lattice and show it can be distinguished from other type of charge order states such as Wigner crystals.