Perfect Coulomb drag in a dipolar excitonic insulator

Understand

Excitonic insulators (EIs), arising in semiconductors when the electron-hole binding energy exceeds the band gap, are a solid-state prototype for bosonic phases of matter.

• Unlike the charged excitations that are frozen and unable to transport current, the neutral electron-hole pairs (excitons) are free to move in EIs.
• However, it is intrinsically difficult to demonstrate exciton transport in bulk EI candidates.
• The recently emerged dipolar EIs based on Coulomb-coupled atomic double layers open the possibility to realize exciton transport across the insulator because separate electrical contacts can be made to the electron and hole layers.