Anomalous Supercurrents in exciton-condensate/normal-barrier/exciton-condensate (EC/N/EC) junctions

The exciton-condensate/normal-barrier/exciton-condensate (EC/N/EC) junction in a bilayer consist of a normal barrier sandwiched between two exciton condensates (ECs), while the two ECs retain a relative phase of φ0. It is a setup inspired by the superconducting Josephson junction but with a special ingredient – the interlayer tunneling. In EC/N/EC junctions of short-barrier, fractional solitons with topological charge Q = φ0/2π are predicted to occur. In this paper, however, we focus on the case that the barrier length dJ is larger than the excitonic coherence length ξ. We find that the supercurrent occurs because of a distinctive mechanism – an Andreev reflection occurs in one of the EC/N interfaces along with the interlayer tunneling in the barrier. This exotic mechanism gives rise to only a half portion of a fractional soliton that carries a doubled topological charge 2Q = φ0/π (for the same relative phase φ0). The distinction in topology between the EC/N/EC junctions of short- and long-barrier is reflected in the supercurrents and their current phase relations, which can be observed directly by experiments.