Researchers observe superfluid-insulator transition in bilayer graphene excitons

One of the defining features of Bose–Einstein condensation is superfluidity, a state in which a bosonic fluid flows without viscosity or dissipation; this behavior has been established in systems ranging from liquid helium to engineered platforms such as bilayer excitons and ultracold atoms. Theoretically, strong interactions within a condensate can stabilize an even more exotic ground state – a supersolid – that combines the crystalline density modulation of a solid with the phase coherence and frictionless flow of a superfluid, but realizing such a state in a naturally occurring material without an externally imposed lattice potential has remained an outstanding challenge in condensed-matter physics.

Researchers from Columbia University, Brown University, University of Texas at Austin and the National Institute for Materials Science have observed a unique quantum phase transition in bilayer graphene, where an excitonic superfluid abruptly becomes an insulator, offering strong evidence for an interaction-driven exciton solid and a realistic pathway to a supersolid phase in a solid-state platform. One of the defining features of Bose–Einstein condensation is superfluidity, a state in which a bosonic fluid flows without viscosity or dissipation; this behavior has been established in systems ranging from liquid helium to engineered platforms such as bilayer excitons and ultracold atoms. Theoretically, strong interactions within a condensate can stabilize an even more exotic ground state – a supersolid – that combines the crystalline density modulation of a solid with the phase coherence and frictionless flow of a superfluid, but realizing such a state in a naturally occurring material without an externally imposed lattice potential has remained an outstanding challenge in condensed-matter physics.

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