Imaging Double-Layer Quantum Hall Exciton Condensates – Part II

When double-layer two-dimensional electron gases are subjected to perpendicular magnetic fields, interlayer excitons can form between partially filled Landau levels. At sufficiently low temperatures, these excitons can undergo Bose–Einstein condensation (BEC). This coherent collective electronic state is expected to exhibit superfluidity and its low-energy charge excitations are vortices and antivortices, in which the layer pseudospin winds by ± π. These vortices are theoretically predicted to carry fractional charge and form a honeycomb lattice [1]. 

In this second of two consecutive talks, we present how high-resolution scanning tunneling microscopy and spectroscopy (STM/STS) can be leveraged to study exciton condensates with atomic-scale spatial resolution, potentially enabling the direct imaging of such a vortex lattice. We observe residual excitonic gaps as the system is doped away from integer total filling factors and investigate the phase transitions between emergent correlated states near these residual gaps. Our results suggest an alternative experimental route to demonstrating global phase coherence in excitonic condensates.