Josephson effect as signature of electron-hole superfluidity in bilayers of van der Waals heterostructures

TL;DR

This paper demonstrates that Josephson effects in electron-hole superfluid bilayers of van der Waals heterostructures serve as clear signatures of superfluidity and reveal the BCS-BEC crossover physics, enabling experimental boundary detection.

Contribution

It introduces the use of Josephson junctions in TMD heterostructures to identify superfluidity and explore BCS-BEC crossover physics in semiconductor systems.

Findings

Critical tunneling current confirms superfluidity.

Maximum critical velocity occurs at BEC to BCS-BEC crossover boundary.

Experimental method to locate the crossover boundary in semiconductors.

Abstract

We investigate a Josephson junction in an electron-hole superfluid in a double layer TMD heterostructure. Observation of a critical tunneling current is a clear signature of superfluidity. In addition, we find the BCS-BEC crossover physics in the narrow barrier region controls the critical current across the entire system. The corresponding critical velocity, which is measurable in this system, has a maximum when the excitations pass from bosonic to fermionic. Remarkably, this occurs for the density at the boundary of the BEC to BCS-BEC crossover regime determined from the condensate fraction. This provides, for the first time in a semiconductor system, an experimental way to determine the position of this boundary.