Quantum Hall ferroelectrics and the hidden link between composite fermions and the exciton condensate
Inti Sodemann (MIT, Cambridge, USA)
In this talk, I will describe two recent developments in our understanding of phases in the quantum Hall regime. In the first part, I will describe our recent discovery of a remarkable connection between the composite fermion metal state realized in half-filled landau levels and the exciton superfluid realized in quantum Hall bilayers. Specifically, I will show that the exciton condensate is identical in all its universal properties to an interlayer paired state of composite fermions, and the two states can be connected in an analogous fashion to the BEC-BCS crossover. In the second part, I will describe our recent proposal to realize a “quantum Hall ferroelectric”: an integer quantum Hall state that spontaneously breaks inversion symmetry. I will argue for the ubiquity of these and nematic states in multi-valley systems whose low energy dispersions are anisotropic, and discuss material platforms for these systems.