Crossover between Strongly-coupled and Weakly-coupled Exciton Superfluids

Abstract

In fermionic systems, superconductivity and superfluidity are enabled through the condensation of fermion pairs. The nature of this condensate can be tuned by varying the pairing strength, with weak coupling yielding a BCS-like condensate and strong coupling resulting in a BEC-like process. However, demonstration of this cross-over has remained elusive in electronic systems. Here we study graphene double-layers separated by an atomically thin insulator. Under applied magnetic field, electrons and holes couple across the barrier to form bound magneto-excitons whose pairing strength can be continuously tuned by varying the effective layer separation. Using temperature-dependent Coulomb drag and counter-flow current measurements, we demonstrate the capability to tune the magneto-exciton condensate through the entire weak-coupling to strong-coupling phase diagram. Our results establish magneto-exciton condensates in graphene as a model platform to study the crossover between two Bosonic quantum condensate phases in a solid state system.

7 pages, 3 figures and supplementary materials

References in corpus (7)

• Collective excitations of a degenerate gas at the BEC-BCS crossover
• Observation of pair condensation in the quasi-2D BEC-BCS crossover
• Gate-controlled BCS-BEC crossover in a two-dimensional superconductor
• Models of coherent exciton condensation
• Paired composite fermion phase of quantum Hall bilayers at ν= 1/2 + 1/2
• Trial Wavefunctions for ν= 1/2 + 1/2 Quantum Hall Bilayers
• Composite fermion duality for half-filled multicomponent Landau Levels

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