Quantum oscillations in a dipolar excitonic insulator

Quantum oscillations in magnetization/resistivity are a defining feature of metals subject to an external magnetic field. The phenomenon is generally not expected in insulators without a Fermi surface. The observations of quantum oscillations in Kondo insulating materials have provided a rare counterexample and attracted much theoretical interest. However, because of the limited capability in controlling the properties of bulk correlated materials, the phenomenon in correlated insulators remains poorly understood to date. Here we report the observations of resistivity quantum oscillations in an excitonic insulator with gate-tunable exciton binding and chemical potentials realized in Coulomb-coupled electron-hole double layers. When the cyclotron energy of the electrons/holes is tuned to be comparable to or larger than the exciton binding energy, recurring transitions between excitonic insulators and electron-hole decoupled quantum Hall states are observed. Compressibility measurements show an oscillatory exciton binding energy as a function of magnetic field and electron-hole pair density. Coulomb drag measurements further reveal evidence of quantum oscillations in excitonic insulating states of finite angular momentum. Our results are qualitatively captured by mean-field theory calculations. The study demonstrates a new platform for studying quantum oscillations in correlated insulators.