Physical interpretation of the cos ϕ term and implications for detectors

Theoretical calculations of the total current in a superconductor-barrier-superconductor device based on the conventional tunneling Hamiltonian yield three terms, conventionally termed the Josephson supercurrent or pair current, the quasiparticle current, and the quasiparticle-pair-interference or « cos ϕ » current. When reconciled, existing theories predict relative signs of the quasiparticle and quasiparticle-pair currents which are opposite to the results of recent experiments which purport to demonstrate the existence and properties of the latter current. This discrepancy remains unresolved. The cos ϕ current (whatever its sign) is not expected to give rise to qualitatively new and striking phenomena in Josephson devices, but may quantitatively affect the dynamical and fluctuation behavior of these devices in a variety of ways