Anomalous drag and charge density order in Double Bilayer Graphene

A unique feature for bilayer graphene (BLG) is the complex landscape of broken symmetry states characterized by orbital and valley orders. Phase transitions between different ground states can be induced with a perpendicular electric field. It has recently been demonstrated that the stability of the exciton condensate in double BLG depends on the combination of orbital and valley order [1,2]. Here we report a novel interlayer correlated phase when one of the BLG is at the threshold of an orbital polarization transition. Using Coulomb drag measurements to characterize interlayer coupling, the anomalous drag response shows the distinctive nature of the novel ground state compared to the exciton condensate. We studied the temperature and magnetic field dependence of the anomalous drag signal, and explored possible ground state for this novel phase, including an interlayer correlated charge density wave state.

[1] J. I. A. Li, et.al., Nat. Phys., 13, 751-755, 2017.
[2] X. Liu, et.al, Nat. Phys., 13, 746-750, 2017.