Kavli Affiliate: Feng Wang
| First 5 Authors: Ruishi Qi, Andrew Y. Joe, Zuocheng Zhang, Jingxu Xie, Qixin Feng
| Summary:
Strongly coupled two-dimensional electron-hole bilayers can give rise to
novel quantum Bosonic states: electrons and holes in electrically isolated
layers can pair into interlayer excitons, which can form a Bose-Einstein
condensate below a critical temperature at zero magnetic field. This state is
predicted to feature perfect Coulomb drag, where a current in one layer must be
accompanied by an equal but opposite current in the other, and counterflow
superconductivity, where the excitons form a superfluid with zero viscosity.
Electron-hole bilayers in the strong coupling limit with an excitonic insulator
ground state have been recently achieved in semiconducting transition metal
dichalcogenide heterostructures, but direct electrical transport measurements
remain challenging. Here we use a novel optical spectroscopy to probe the
electrical transport of correlated electron-hole fluids in MoSe2/hBN/WSe2
heterostructures. We observe perfect Coulomb drag in the excitonic insulator
phase up to a temperature as high as ~15K. Strongly correlated electron and
hole transport is also observed at unbalanced electron and hole densities,
although the Coulomb drag is not perfect anymore. Meanwhile, the counterflow
resistance of interlayer excitons remains finite. These results indicate the
formation of an exciton gas in the excitonic insulator which does not
condensate into a superfluid at low temperature. Our work also demonstrates
that dynamic optical spectroscopy provides a powerful tool for probing novel
exciton transport behavior and possible exciton superfluidity in correlated
quantum electron-hole fluids.
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